There should be new randomly generated dungeons kind of similar to the Aether II dungeons, that are really big and have bosses. The Ender Dragon and Wither are getting kind of boring, so Mojang should add expanded dungeons!
More multiplayer fun!
Cave exploring is a little more suspenseful! (Will you find one, or not?)
Minecraft in general would extend!
More mobs, some for certain types of dungeons! (EX: Fire dungeon, fire mobs)