As someone whose characters include robots, aliens, jackalopes, and scrub jay/cougar hybrids, I'd love to see something beyond the standard single-species pack/pride/clan groups. It' a bit of a paradoxical problem, though... people who try to make more unusual RPs tend to give up due to lack of interest, and those inclined toward less common character types usually seem to ultimately give up and make a wolf/lion or just sit around on the plains because they can't find RPs. Heck, even at the best of times more creativity means it will be hard to find a group that your particular brand of strange or unusual character will fit into.
I can kind of see why people would have an instant adverse reaction to a slave RP, though. I'm sure it was perfectly harmless, but there ARE a lot of potential negative (and sometimes inappropriate) connotations people might automatically jump to with something like that.
