I honestly don't think there's really any character I'm necessarily against, it's just I think some characters would feel out of place depending on their circumstances.
Like for instance, Shadow I'd be down for, but I'd feel it's extremely odd if you didn't have some form of Tails, Metal Sonic, or even Robotnik present in the roster, AT, or game somehow. (I'm not exactly counting Green Hill Zone btw.)
Same thing with Rex and Pyra, but for a completely different reason. Like I think for someone completely unfamiliar with Xenoblade sees both Shulk and them next to each other, it'll feel completely off and confusing given their separate and very distinct art styles.
That's why for their inclusion, I'm honestly curious if they would still be in their respective art style or try to bring them closer to Chronicles and X's style.
I'm honestly not against anyone getting in, like come on look at the characters I support, it's just some would be odd inclusions to me dependent on their circumstances. Despite that, I'd be perfectly fine with anyone who gets in though