It would be cool if travelling far enough in one direction eventually looped back to where you started, based on your chosen world size. That's all you'd have to change, I'm not asking to actually make the blocks curve away to a horizon or let you mine straight through and back out the other side or anything, just a simple looping mechanism on the cardinal axes. Instead of negative coordinates if you go beyond zero the next block would be at the world size-1 (so, if you choose a 100k block world size, and you headed east you would go: 2 -> 1 -> 0 -> 99,999 -> 99,998...).