Awesome feature! Just to to throw something out there, it would be hilarious if monsters would randomly use different varieties of their class of weapons: the big flying tick could occasionally shoot speed/fire/ missles, gunners could randomly fire off an annhilator blast... Also, tack "Fiend from Quake 1" to my wishlist. Imagine the time someone spamming explosives would have when one of these guys lunges at them. The mutant just ain't the same.
Also, it's great to hear that you've got an implimentation method nailed down for working with different models. I don't think there's any way a Mac guy can program entity behavior, but I'd be interested in trying to build some new monster and weapon models. Would you be interested in re-skins for the different weapon variations?