How about, since this is a steampunk dimension, a train?
Once you've obtained dragon breath you can use it on a minecart with furnace. The furnace will burn brightly, and then it will shoot forward pushing any minecarts ahead of it with it, including any players or mobs within. After about maybe 50 blocks, the train will be teleported to a safe location in the new dimension. This can be repeated to go between dimensions, and you can find dragon breath in some chests in the new dimension (so you don't become stuck). However, as you explore the dimension, you can find materials to build a Hyperspeed Engine that can be used to build a minecart that can swap between dimensions at will and doesn't require fuel or track (however it cannot be used for travel within the dimensions).
What about making it so acessing the new dimension involves breaching the top Nether bedrock? Then, the Player would have to build a "portal" of sorts with an Detector Rail on top of Bedrock that has to be made above y:64 in the Nether and Iron Blocks.
Breaching the top Bedrock layer of the Nether could involve a new block that is made from Shulker Boxes (Or at least Blaze Rods) and TNT. If the former, there would also be Ender Pearls in the recipe. If the latter, there would be 1 Nether Star. The new block (Placeholder name: Shulker TNT) would destroy all blocks above y=2 in a 3*3*3 radius, causing all of them but Bedrock to drop.
A lot of people don't like modernized cars and planes, but if we had some Kerbal Space Program style construction, rather than building the same 3 models of planes, cars or trains, I think this would fit better with the Minecraft theme. (They also shouldn't be called cars, planes or trains. How about "apparatuses" or "flying machines"? Although trains might actually fit.)
Alternatively, the player could build armored walking mechs, which might fit better with the steampunk style.
Would we have to introduce new ores into this dimension? I'm thinking copper or zinc could be used to make brass, which would then be used for steampunk things like the mech suits or vehicles.
I was thinking of precisely the KSP-style construction... I should have mentioned it explicitly. However, I wouldn't recommend calling them "apparatuses" or "flying machines" because that would only be insistent terminology. Of course, the more technical names such as "Aerodyne" (Both for planes, helicopters, whatever people would invent due to the DIY mechanics) for heavier-than-air aircraft. Of course, giving the players ONLY the parts' names and letting them make up the names they like would be the most likely result.
New ores would allow more more building potential, and could be used for some of the parts and several new items.
Something else to consider with a new dimension is the color scheme. This may sound silly, but here me out.
The Nether has a color scheme of crimson red, and orange/yellow. The End has a color scheme of black, purple, and bright yellow (endstone).
So, what would the color scheme of the new dimension be? Personally, I would really like it if one of the main colors was green, though if it were steampunk it would probably have to include gray/grey or brown too.
Fishg, you are 10000000000000% right on that. Adding more end-game content at the moment would already be pushing it, as you can get fully-enchanted diamond armor so early on compared to how far away the elytra is. I think we should preserve the Diamond Armor, and the enchanting too, but we need to space it out more and maybe make different "tiers" of diamond armor.
What do I mean by that? Well, first we should start by making it so that the player doesn't get full iron armor the first or second night. It's kind of silly how easy it is to get; it gets to the point where the default player is with the armor points of full iron armor, since it is so easy and to obtain. My proposal is that we make either iron ore smelt into 3-4 iron nuggets, or we make iron gear require more iron to make. Maybe iron ore that smelts into ingots could be found deeper, too, so that if you're already at the point of iron armor you can easily get more of it in case you want to make hoppers, cauldrons, anvils, etc.
Now for how we could add "tiers" of diamond armor. The concept as already been partially implemented with having different levels of enchantments (Protection I, II, III, & IV), but just like getting leather and getting iron, they aren't really spaced out. We could potentially make it so that the player has to start out using just Protection I, and then has to get new items to use in place of lapis in order to get higher versions of enchantments.
Another Idea for a Dimension!
This idea is something I've thought about for a while but haven't shared. What if there was an "Eternal Sea" dimension, maybe like Davy Jone's Locker or something? I don't know how you'd access it; maybe if you die at the bottom of a really deep ocean, or maybe if you fail to defeat some sort of new boss. (Though, if you went to an "Eternal Sea" after being eaten by a Kraken sort of thing, it'd be completely ripping off Pirates of the Caribbean.)
Anyway, I am really excited for the thread. I can't wait to see the amazing ideas we come up with, and maybe even get put in the game!
The general colour scheme could be a mix of brass-like, metallic gray, rusty red, and green. Generally, rather than making it fully steampunk, it could be made into a mix of Steampunk, Dieselpunk, raygun gothic (With some zeerust elements) and even traces of Nanopunk and biopunk (Mostly so the enemies aren't all robots).
As for retiering, Diamonds could be more common and have a smaller gap in relation to iron tools. Rather than outright reducing Iron Ore smelting output (Which would be awful for people who are harvesting it for other uses), there could be more iron sources, but less iron overall. For instance, iron would tend to spawn in a few large clusters, rather than spread out, meaning that there's a few spots with a lot of it (Iron clusters could tend to spawn in Extreme Hills, there could be some surface iron ore in swamps...), and apart from that, there would be less iron in the average chunk, which would be compensated by making some mobs drop Iron Nuggets on death (For instance, a mob that spawns with equipment could drop 1-3 nuggets for each ingot that would be needed to craft the gear they're carrying, so, for instance, a Skeleton that spawns with a gold chestplate would drop 8-24 Gold Nuggets; with chain pieces only dropping up to 1 nugget per ingot that would be needed if Chain Armor was crafted from Iron Ingots, meaning that a mob in full chain armor would only drop up to 24 Iron Nuggets. Other sources could be making Zombies drop iron nuggets 33% of the time, being able to harvest iron nuggets from the water is swamps...).
If we're adding more end-game content, then we need to add more end-game threats. The thing about Minecraft is that the difficulty kinda stays the same. (I think there may be regional difficulty or something like that, but I don't know a lot about it.)
In Terraria, for those who don't know, you slowly progress through the start of the game in a sort of "Easy Mode". Once you defeat a difficult boss (The Wall of Flesh) you can move on to a new mode, the unsurprisingly named "Hard Mode". In which, evil biomes spread across the landscape, requiring you to contain them, harder enemies spawn, and you can do more exciting stuff.
I'm not sure Minecraft really needs a "Hard Mode", but maybe the difficulty could progressively increase in smaller ways as the player gets Advancements or as time goes on. Mobs should spawn with more armor and more powerful weapons, mobs can see players from further away, etc. The only problem with that is that on servers, if the difficulty is based on the player, an experienced player could go near spawn and a bunch of difficult mobs would start tearing apart newly spawned players. (And this problem gets worse if the difficulty is world-based, because then new players deal with incredibly hard mobs when joining an old server.)
But the reason for me bringing up Hard Mode or Progressive Difficulty in the first place, is that if we want to add a new dimension with end-game stuff, we need something to give good reason for this new stuff. The one good reason many Gun threads get turned down is because the Bow is already capable of doing significant damage, and in order to make the gun powerful enough to make it worth using, it has to be incredibly overpowered. The same thing can be said about vehicles (or most modern objects), ridable dragons, and many more things.
Apart from that, there could be Advancement-based mobs, such as, say, a flying Overworld mob that only spawns if you have found Elytra, or skeletons that spawn with new ranged weapons from the 4th dimension once said weapons have been found.
As for implementing a "Hard Mode" in servers, it could be made so that the new mobs only spawn at least X chunks away from spawn.
We should be able to bypass this problem with the new dimension. Since players have the choice of when to enter it, we don't have to worry about early game players getting destroyed by very dangerous mobs. We can assume that everyone coming to this dimension has enchanted diamond. An example of this is the Divine RPG mod, which has 5 dimensions that progressively get harder and require you going to the previous dimension first. I'm not saying we need 5 dimensions, but this sort of "new dimension = more difficulty" idea would work well here.
I completely agree that the current system is a bit too simple. While I'm open to a such a game-changing overhaul to the Overworld, I believe there may be a far easier alternative. Going off the idea that this dimension will contain harder mobs, how about we simply add another armor set obtainable from this dimension. Say the "zombie" of this dimension is 4x as powerful. Enchanted diamond would be the equivalent of iron here.
We could take advantage of a possible steampunk theme by changing this dimension's progression to be more about building "gadgets", rather than smelting materials found from caves. You'd have the scavenge through the dimension to gain parts, and then put them together to create new "gadgets", such as crossbows, booster boots, or x-ray goggles. It might sound moddy, but I think with some effort and the vanilla game intended it could work.
The only foreseeable problem with this is that even more powerful weapons would make the Overworld a joke. However, if the player has already defeated the End they already are very powerful, and as long as Overworld materials (such as diamonds) aren't required in the new recipes, mining in the Overworld will become useless. I think it would be neat for the Overworld to transition through the game into a "peaceful" biome, with most of gathering and combat taking place in the other three dimensions.
When I first read this I really liked this, but the more I think about this the more my doubt grows. If this only attained thorough failure, will it come across annoying rather than exciting? It seems just like another tedious step. Also, just how much would be in the dimension? If there's a lot of cool stuff going on in here, will players purposefully die just to enter the Eternal Seas? Still, I wouldn't be against this being our final product.
Making the progression in the new dimension revolve around obtaining items that provide the Player with new abilities and gameplay mechanics would be more original than making them get even more outright powerful gear, so making it revolve around "gadgets" seems like a good idea.