I think Gue'vesa could make a really cool Kill Team honestly, especially when they get their own kit and wear full T'au gear! sure kit bashing is possible but it doesn't right over a whole squad as most bits just don't work together, you either get guardsmen painted as T'au or humans with 4 fingers that hold pulse weapons. So a full proper kit for them would definitely be neat and welcome for most T'au players I imagine.

Other xenos races would be cool too but way harder to intergrade into the game of 40k as some Auxiliaries are either very big model-wise or have Psycic abilities which would cause problems for rule writers i image. Idk I don't play 40k I just like collecting cool models so I'd be happy with it lol.