along with a 3rd shoe-in in my opinion... Meowscarada.
I read opinions about how 'the ship will have sailed' by the time Smash 6 comes out but imo Meowscarada has stood the test of Gen 9 enough to warrant a spot in the roster (better than Incineroar in its own Gen I'd say). Not to mention that there's the anime to consider too, which will increase its prominence by a lot and its overall popularity, plus, let's be real, it's Pokémon, a newcomer is absolutely coming, I think Meowscarada fits that slot perfectly and completes the trio of characters I would bet money on seeing in the next game.
For Gen 9 to even have a chance, the next Smash would have to had its roster mapped out before Scarlet and Violet had been released and a slot reserved for a Pokémon from the next upcoming Generation, to which Gen 9 would be the upcoming one.
This is literally what happened with Gen 4 (with the added bonus that Lucario's movie would be airing in theaters within weeks of when Brawl's roster would be drafted).
This is what happened with Gen 6, with Sakurai even requiring concept art for a Pokémon that hadn't been even given an OFFICIAL NAME yet.
And this is what happened with Gen 7, this time with pre-release videos showcasing new Pokémon being readily available before he made his final decision closer to Sun & Moon's release.
With that in mind, a hypothetical Gen 9 Pokémon would have been decided on well before any "test of time". Based solely on their concept as a fighter.
Meowscarada is only but a single possible option in this scenario. It having "popularity" or "anime prominence" or "marketing" (which isn't exclusive to it by any means) is ultimately irrelevant since none of it would play any factor when a Gen 9 Pokémon would be hypothetically picked.
Meowscarada needs:
-for Smash to have its design document finalized before Scarlet and Violet (which may or may not be the case because we know Sakurai has an undisclosed project that had its design document drafted in July of 2021, but there's no guarantee it's Smash)
-to appeal to Sakurai the most on a conceptual level, with the likes of Quaquaval, Tinkaton, and Ceruledge being just a few examples of very stiff competition
So no, Meowscarada is not a "shoo-in" by any stretch.
It is a
possible option (if timing is right), but not the
only option.