This post may be a hot take but here we go. I keep on reading people all around the Internet saying they would be disappointed if there are no regional forms for the starters.
I'd say that they aren't likely to happen, but just megas, given how this is set in present day and lore-wise it doesn't make sense for Bayleef, Croconaw nor Pignite to evolve into a Kalosian regional form as it would require a retcon because they weren't able to do so in X/Y (by having been transfered from BW or BW2).
Not only that, but the excuse lore-wise in PLA for Quilava, Dartrix and Dewott to evolve into regional forms was Hisui's harsh conditions, which made compulsory for those Pokémon to adapt themselves in order to survive. Here in Lumiose City there doesn't seem to be any particular, special condition, because Quasartico INC. in fact is making the city's environment adapt itself to Pokémon and not the other way round.
Also, if any new regional form was to be introduced, it would remove some spotlight from megas, which are the new designs to shine this time around. So, well, I wouldn't be mad at GF if we only got new megas, but a good amount of them, as this is PLZA's whole point.
Regional forms can wait for Gen 10 or another Legends games with a different setting.