Rex was almost added since he was from the most recent Xeno, but Smash was too far into development to add him in the base game so he got a costume. XC2 is represented in Smash with that costume and spirits of basically the entire playable party. I think it might have some songs as well though I'm not sure.
XCX meanwhile only has spirits in Smash, and just a handful as well. I've said this many times, but when Ultimate was being made Xeno wasn't a popular series. Smash gave Shulk a spot which helped, then XC2 blew up which helped even more, and then Torna came out which continued that. Now that XCDE came out, only XCX is missing on Switch and like I've said, leaving that game to die on Wii U is really fuckin' dumb of Nintendo. Most big first party games were ported, they should use the popularity that the franchise is getting at the moment to port that one too. Elma would be the perfect rep for it and a perfect second rep for the XC series.
The part about Monolith not considering a port is pretty old too, I think it's from 2018, but he just said that it would be expensive and this was at a time when XC series didn't have that much attention like it does now, it was certainly building at the time since XC2 had come out and done very well . XCDE just launched, and we have confirmation that they were working on a new game alongside it. So if anything, maybe the protag of the new Xeno game could be a pick, I don't know. Either way, the director of Monolith has confirmed that he gets a lot of requests about XCX so I definitely think it'll get a port and even a sequel.
