I love all of those ideas.
I saw the post about having a main world nether when it came out, and I thought that would be really neat too, especially what with all of the awesome builds people would come up with.
The quests idea is also my favourite. A friend of mine has heavily discussed the idea of having quests on Munchy surv with me, and I honestly believe it would be a really fun dynamic to add to the general gameplay.
The tag sounds cool too. 