Anyone that's seen an ilmango video knows that Minecraft is capable, right now, of some pretty crazy automation. Those people will also know that that automation almost always requires some redstone and gametick trickery. While this 'trickery' tend to be confirmed as 'intended functionality,' it's always with a wink. If you could add just two things, two blocks, with a mod, to make all of this feel like a fair part of the game, what would they be?
A Block Breaker
"A tired idea." "Every complicated automation mod has it." "Only for those nerdy people that watch direwolf20 or whoever."
It doesn't have to be complicated. At most, you would have coal to fuel it and tools that need to be replaced in the block's inventory. In any case, the idea is that it will break the block in front when powered by redstone. To be balanced, you might have the block breaking be timed, equal or related to player mining times for that particular block. To be fair, you wouldn't have it pick up the destroyed block's item drop.
A Block Placer
The other side of the idea would be to place blocks. Overall, an even simpler idea. When powered with redstone, it places the first block/item-of-a-block in front of the block placer. Beyond that, it should also be capable of planting seeds on farmland, to be fair. Non-place-able items should either clog up or be 'dispensed,' making the block function as a dispenser.
Why not more? It'd be a mod, so you could have upgrades, and...
I want a vanilla feel. Redstone, observers, dispensers... these two blocks are clear logical progressions of what we already have. If it doesn't feel vanilla, the idea isn't being done it's simplistic justice. Moreover, it probably sounds like I'd want this in vanilla minecraft. Wouldn't you? It'd be a lot more plausible if there were a mod to demonstrate the repercussions/etc. of adding such things, and in a vanilla style.