Hmm...
You know, I'm going to try to make my own mod, and I hadn't seen this thread before. (Looking for feedback on it, by the way.)
Honestly, one of the things I want to do, however, is move away from the sort of Tolkienian fantasy world, especially where every race is a xenophobic always-one-race version.
Really, looking at these, though, the castes just seem to be good/evil versions of the same thing. I can't say I really care for simply cookie-cuttering "always chaotic evil" over everything, at least, not without some kind of overarching storyline that would help explain it. (Some version of a zombie virus that forces a certain ethos.)
I like adding different races in principle, but I'd rather they have a social impact on the creatures that are already there, rather than simply being "oh, and this, too".
... then again, having said that, I can see some places where the same can be said for my own idea. Well, that's something to revise, then. I should put in more effort to create original species.
edit: Sorry, as I hit post, I realized I was only highlighting the percieved negatives... I definitely support, at least, the basic idea of this, it's just that it doesn't quite match my tastes in fantasy.