I guess the main things you could do with it from here involve temperature-related stuff, as you say, and evil. Rainforests when temperature and rainfall are both over a certain amount, coniferous forests in very low temperature areas could be taigas, maybe there could be mangrove forests in hot, swampy areas. A few different kinds of grassland, as you say- savannahs when the temperature is high and steppes when it's low or something like that.
There's a lot you could do with the evil thing- at the moment, hills and grasslands seem to be missing evil versions. Although I can't think what they would be called...
Another idea is that if evil is at or close to maximum, you might get special terrains that were one level beyond the other evil terrains. For example, Haunted Woods, Hellish Wastelands, Cursed Fens... you could use those names or come up with your own, but anyway, these could have especially powerful and nasty inhabitants, maybe some found nowhere else. And various weird special things could happen there...
The reverse could exist as well, if evil was at or almost at zero- Sacred Forests, Blessed Plains, that sort of thing. All this would be probably be major bloat stuff though...
On the evil note, are swamps only possible when evil is over a certain level? That doesn't quite seem right... maybe it could be that they're called wetlands at EV<66.