3. Introduce a new movable unbreakable counterpart to obsidian.
Simple. You now have an indestructible base from the outside if discovered
If your base is covered in bedrock, you're not in vanilla/survival anyway. So you can use all kinds of methods, such as any of 100s of mods/plug-ins to allow protected areas.
If the block is movable, what is to prevent others from moving it? it doesn't make it secure.
Vanilla Minecraft is not designed to stop all attempts at getting into places - if it was, that would cause a lot of problems. For one thing, it'd give the griefers another way to cause huge issues, such as just blocking spawn entirely.
Best way to handle griefers is, don't let them on your server.
If you're on a server with people following the rules, you shouldn't be worried about your base being secure.
And honestly, no matter what you do, it'll never really be secure. There are always ways around things... such as enderpearling in or whatever.
because you can trap people in a box made of unbreakable material and they will never be able to get out until YOU let them out.
And that's the worst thing you can do to anything ever.
You can already do this with stone and pistons, if you can capture the person without a pick. That's one of the reasons the /kill command exists. Also, multiplayer servers have moderators who can ban people that do stuff like that, and if you're just playing with friends and one of them traps you for an extended period of time, I think it might be time to re-think who you call friend or at least who you play Minecraft with.
In general, I think you can't use the possibility of griefing as opposition to an idea, because the game is already filled with ways to grief, and servers use plugins to prevent it or (in rarer cases) moderators to encourage friendly play.
I'd say no to moving bedrock with pistons for two reasons:
1.) Bedrock is supposed to be unmovable in survival. If you intend to break or move it, you may as well just go to creative mode because that is considered cheating. All existing methods of breaking bedrock in survival are exploits and the development team plans to remove them at the first chance they get.
2.) It accomplishes nothing. Say you build a house with bedrock by using pistons to move it. What's to stop your opponent from using pistons to break into your house? All it will do is delay them or possibly make it more trouble than it's worth, and you can use obsidian for that already.
I'd say no to moving obsidian because it actually makes better house armor when it can't be moved with pistons. I'm rooting for home defense, here.
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I want ocean content, nether biomes, and savanna passive mobs.
All existing methods of breaking bedrock in survival are exploits and the development team plans to remove them at the first chance they get.
I agree with most of what you wrote, but not that part.
There have been lots of ways to break bedrock, for many many years. Some have been patched, and other ways were found almost immediately.
It's become a joke between devs and the community. They might patch one or two ways of doing it, but it's not a high priority. I know of at least 6 reasonably simple (but totally different) ways to do it in 1.12.1, and I'm sure there's more than that. (Dragon egg, TNT cart, nether portal, mushroom, Ender crystal... some more I won't mention because I think it's not widely known)
I doubt it'll ever be properly patched.
Most people don't mind it, anyway; a lot of us think it is very convenient to be able to bust through the top of the nether. Of course, if you choose not to use such an 'exploit', that's fine too; but it really does very little harm; it just means neater access to things we might construct up there - and it's a way down for anyone who somehow glitches through the top as well.
It's nowhere near as troublesome as duplication exploits, and several of those have remained as open/recognised bugs for years. (Falling block duplication, donkey/end portals, rail/fast piston, looped hoppers on chunk boundary... and several more)