Didn’t X do better in the West though? I think Sakurai takes worldwide appeal into account (which is also why he didn’t make Takamaru playable — very few people outside of Japan are familiar with him)
X did decent sales wise, considering it was released on the WiiU, but well X in general is a major basebreaker. Like people complain about XB2's character designs I guess, but X caused a major split in the overall fanbase, because of how different it was.
DarkFalcon
even if Rex & Pyra's concept art was finished in 2016, they can still be a Greninja situation, but they need alot of luck.
If Rex & Pyra are at base Sakurai had to be aware of the game in 2015, which is not impossible, because in 2015 it was pretty clear that Nintendo was going to shift to Switch development behind the scenes and thats why 2015 was such a drought year, plus Sakurai had to get in touch again with Monolith anyway to get the rights for Shulk (Sakurai stated in an interview, that he also needs to get licenses for all First parties) and Monolith and Sakurai are pretty close in general, because people forget that Monolith was very involved with the development for Brawl.
So yeah if Monolith did tell Sakurai they where working on a new game, that was planned to be released in the first year of the Switch and told him about the stuff like how the gameplay could work or something like that, is it really that farfetched that Sakurai liked the idea and reserved a slot for this Xenorep? However Monolith does need to show the finalized or near finalized design for Rex & Pyra somewhere in 2016 + Xenoblade 2 gameplay, because the Mewtwo DLC showed us, that it takes 6 months to create an unique character from scratch and Its safe to say that other Xenoblade 2 content will be very scarce then like no stage(The Castlevania stage took 1 year to develop for example and I feel in 2016, they rather want to start focusing on making the game presentable for E3), and perhaps a few music tracks (like Corrin in Smash 4)
Its also not the first time this happend in the franchise, because the same scenario happend in Brawl. Brawl's roster was decided in 2005, minus Sonic and Wolf(if he was considerd in 2005, he was dropped from the draft stage very early on).
In 2006 or 2007 Sonic won that poll, so Sakurai did all he could do to finish Sonic, but he had to make several sacrifices to make it happen. These sacrifices where needing to cut characters who where not finished yet (which where Jigglypuff, Toon Link, Roy & Mewtwo). This brings us to our friend Wolf. Unlike Mewtwo & Roy, Wolf lacks a scrapped unique victory theme and in the Brawl data always is the last character plus if I recall correctly his overall data also is after the slots that contained the forbidden 7 data (need clarification on that though), but yeah Wolf was created in 2006 or 2007 and is considered a unique character.
TL.DR version, Rex & Pyra can be a greninja situation, but Sakurai has to have knowledge of XB2 being developed in 2015 and Monolith had to show near finalised content of that game to Sakurai in 2016, other Xenoblade 2 content minus music tracks will not be in the game and Rex & Pyra need to be the last character finished in the overal data, to make this theory come true.
Although do note I'm more expecting no Xenoblade rep at base and Rex & Pyra as DLC.
