So three future updates are going to update each of these three biomes? I really hope the performance gets a look because it just keeps getting worse, but you miss out on a lot not to update.
I'm surprises the Savanna biome is in that list. The Taiga and Desert biomes I understand, but the Savanna isn't that old, relatively, and already has the unique feature of a unique tree and wood type, as well as terrain (and that's not even including the Savanna M biome). I'm also not sure how I feel about termites, although the new tree is nice (doubly so if it's a new wood type, speaking as a builder).
I'm not opposed to it getting an update, mind you, but I'd have rather seen some other biome get the treatment before it. Plains, Extreme Hills, and Forest biomes are some such examples. Plains, in my opinion, need to be bigger, a bit more flat, and then have some unique things added to them. They feel more like glorified hilly meadows as it is now, that people only build in because they're the flattest and most cleared of obstacles. That's not a bad thing, but I'd like to see them be more.
Mojang has the statistics on what biomes players spend the most/least time in, so I think it's likely they chose the Desert, Savannah, and the Taiga biomes because they were the three non-subbiome biomes that were frequented/lived-in as the other ones, not based on how old the biomes are.