Played both games and I can totally see Saki having a very unique moveset when switching between the sword and cannon to control space and move in and out of the opponent's range.
Season 1 DLC is pretty much all 3rd party, that's just a given at this point, but I truly believe that Saki will be in season 2, since I'm expecting that to be more focused on 1st and 2nd party titles under Nintendo. Saki's absence as an assist leaves me with hope, especially since he was acknowledged enough to be made into a costume.
I also won't ever forget that Sakurai did wanna put him in Brawl, but settled to make him an assist.
Saki is definitely one of those assists that will translate very well into a playable character, as they already have a start with his moveset like they did with Mac, it's just a perfect fit. As an assist, Saki was one of the mobile ones that threw out attacks and combos and really seemed like he could've been made playable with just a bit more time, and he was really the perfect size to be a playable character.
I still believe he can get it, won't stop thinking so until the end.