As many of us know, the next update will include a Nether reset, which will allow gamers unlimited access to glowstone and nether brick (since you can reset after you've mined them all). It will also allow gamers whose world was generated before the second to last update to have access to Nether Fortresses and all that comes with them (nether brick, nether wart and blaze spawners).
What I would truly love, however, is the option to do a partial overworld reset. This could be accomplished by selecting parts of the map that you want "reset" and parts of the map that you want "protected"--obviously the areas you've built on would be "protected". This would no doubt be complicated, particularly with respect to how the "reset" lands would merge with the "protected" lands, but this could be accomplished. I highly doubt it would ever happen, but that's why I call it a "fantasy function."
Something that I've mentioned before which would be easier to program is a third portal (after the nether and end portals) that would transport the gamer to another seed (or the same seed with an entire "reset"). This was, gamers could access new terrain features like jungle without having to start a whole new world. At least for single player this would not create any additional load on the console, since it is loading only one world at a time. Multiplayer would probably be the problem here, especially when the individuals are on the same console, since two worlds would be rendered simultaneously (this is done with the Nether, but that is much smaller than the overworld).