As I'm sure your aware, Notch said in his blog/twitter that he would be adding new terrain generation features that are unique. But what does this mean exactelly?
is he simply referring to the new ravines, strongholds, towns/giant mushrooms, or is he talking about UNIQUE terrain features such as advanced generation processes, and unique terrain types not yet seen (or more on par with the alpha terrain generator that is)
I've been assuming he is talking about the ravines, npc towns and the like. These definitely would be new features to the terrain generating engine. As far as I know what you have mentioned are all that has been revealed as far as the new terrain bits, and there may be more things beyond that, but anything else would be speculation.
well, there's this quote: “I like the more separate areas of terrain, instead of our [Minecraft's] biomes that kind-of blend into each other. I think it works very well. Because mentally you know where the boundaries are. I haven’t even thought about it this clearly but yeah, I think I got inspired by Terraria. I get inspired by all the games I play.”
notch talking about terraria (http://www.pcgamer.com/2011/07/22/minecraft-could-get-terraria-style-bosses-says-notch/).
so the terrain generator changes+that quote could mean he's changing biomes a little. or not. who knows?