Nothing has been confirmed, but leakers with very credible track records have said they are happening (tho some details don't match as some say they will have Let's Go mechanics and others say no) But mostly it's that everything is lining up. SwSh teased gen 4 with a shop in game having a croagunk statue which is an updated version of ones that could be found in shops in Sinnoh. Pokemon games have had a trend as of late of always having one detail somewhere in the game that hints to what is next. XY had a tiki item that hinted at a Hawaiian inspired gen 7. Sun/Moon had hints at what would be the Let's Go games. Let's go had a map on a wall with an image that looked like an upside down UK, which was a clear hint of Galar...
Plus Gen 4 Remakes are just next in line. It's far too soon for Gen 9 reveals, They could do another wave of DLC for 8 but that would be underwhelming. The only way i see Gen 4 games not getting a remake this fall is if they are skipping a year.
That said i would love to be wrong as a skipped year would mean more time on whatever the next game is and I would rather gen 4 get remade in a generation with a better foundation. Put all focus into making Gen 9 as good as possible, and then have SInnoh remakes build off of that.
That however seems very unlikely, so they are almost certainly getting a small reveal tomorrow. By small reveal I mean some sizzle reel that ends in the logos for the game. GF always does this, tell us what the game is and have us wait months for anything substantial about it.
Anyway, from a marketing standpoint they are going to slowly cool off on promoting Galar to build hype for Sinnoh, so a Galarian rep in Smash is likely not a big priority for them.
Plus, we just Challenger 9 revealed already. I doubt that GF has plans to reveal another Pokémon rep as challenger 10 in tomorrow direct.
I didn;t meant to imply that a pokemon fighter reveal could happen tomorrow, I just meant that the time for a Galar pokemon is likely up since come tomorrow GF will be wanting to put most marketing toward promoting Sinnoh.