A cat riding bears? Not only that, but "WoW needs a new animal race"? What do you call taunka, tauren, satyrs, centaur, qiraji, nerubians, and many more then!?!?!?
Plus, I think they'd need actual lore as to why they joined the alliance. I mean honestly, do you really think one day, BOOM! Tigon would be there, with no particular reason why?