Dude, he has a Chance like DJ Ocatvio for Smash.
Although, if Miyamoto ran Smash Bros (Despite he is old), he could count his Andross' SF Zero Body as Canon cfr Smash, since Andross wouldn't be such a Bad Idea.
First, he would be unique Addition for Roster from Star Fox side;
Second, he could be unorthodox Character along with Virtual Boy in Smash 6 roster;
Third reason, he will be Real Star Fox villain rep, since Wolf is just mockery of Nefarious roles of Star Fox franchise.
This post is making quite a lot of assumptions.
If you're hinging Andross's odds on Miyamoto developing the next title, that's already a bad sign for Andross. Miyamoto stepping in as director for a massive series after four or five successful games is unprecedented, especially considering both Miyamoto's age and that he has no real experience developing something like Smash. I could go into other reasons why Miyamoto being the next director could be a literal Worst Case Scenario, especially for the roster as a whole, but it's such a borderline nonsensical idea that it's not really worth harping on. The point is that if something that out of left field is required to even have Andross be
considered, he's far,
far from being likely...to say nothing of being "the most likely first party villain."
As for the "he would be a unique Star Fox addition" point, I really don't think that's relevant. Pretty much the only time Sakurai went in with the mindset of "I want another character from [x]" was with Zero Suit Samus in Brawl, and Metroid was really big at the time but only had Samus on the Melee roster. Not only would Star Fox's currently near-dead status make this unlikely, but the fact that it already has three characters makes this even less of a concern. Usually, the process starts with "what Nintendo games are big right now," "who are the big fan requests," or "who could fit this concept I've been wanting." Andross doesn't fit neatly into any of those three.
There's also the false absolutism that comes from acting like Andross is the
only unique choice possible. Even if they wanted a Star Fox character that's incredibly different from Fox, Falco, and Wolf (despite the latter two being incredibly distinct by this point), there are also Krystal (who's also the most popular Star Fox pick) and Slippy (who is iconic and could use his drones and other machines). Andross does not hold a monopoly on being the only potentially unique Star Fox character.
You then go on to say the fact that he'd be unorthodox is a boon for him. I don't really see how that's the case. With someone like Wii Fit Trainer, while she was unorthodox, she still had a very clear style to pull from just from looking at her: the use of yoga moves as attacks. Andross is unorthodox in a different way: his actual body type and playstyle are an incoherent mishmash. Confusion over how a potential fighter would fight has historically not been a boon, but rather a bane. Not only was Pac-Man initially ruled out for Brawl due to Sakurai not seeing how his flat pizza form could fight, but Excite Biker being eternally bikebound and the confusion surrounding it was exactly why Sakurai skipped out on them and opted for the Ice Climbers instead.
For your third point, while Wolf is more morally ambiguous than an outright villain, due to his status as a mercenary, it ultimately doesn't really matter in the grand scheme of things. Star Fox lacking a "true villain" isn't something that makes Andross more likely. Again, that's not how characters tend to be picked. The best chance Andross has at getting in is somehow getting Ridley or K. Rool-level fan demand, which at this point he absolutely does not have.