As you may have caught wind of by now, Mojang is taking a vote on which of Minecraft's biomes should be updated next. The vote will take place at MineCon Live on September 28, and the biomes involved include Badlands, Mountain and Swamp. We've already seen what the Badlands update entails. Now, here's a short video on what may come to Swamp:
Should it win the vote, the Swamp biome will get boats with built-in chests, frogs, and a new mangrove tree. For reference, here's what the Badlands update looks like, and here's Mountains.
Of course, it's likely that all of these biomes will get updates in due time: this vote is just on which will come first. So if you're particularly passionate about any of these three biomes, despite none of them being Caves, make sure you vote on September 28.