Anyway, we know these most likely won't be the only variations or new evolutions, so let's speculate on possible evolutions/variations!
Here's some things I think might be possible.
A Glameow evolution that's not Purugly. I'm not gonna say the rake-thin cat's gonna evolve into a more different rake-thin cat, but options for Pokémon food in the past are likely to be more scarce and less fattening. I could see Glameow becoming a more ferocious and agile hunter than the pampered felines of the Poké aughts stuffing their faces with poffins.
More shiny Bronzor. To quote the Platinum Pokédex:
There are researchers who believe this Pokémon reflected like a mirror in the distant past.
I could see this happening.
A separate new evolution for blue Basculin, maybe? The new trailer prominently showed off a Basculin evolution being used to traverse water, but only showed a red Basculin evolution. It could just be another Shellos -> Gastrodon case, but it'd be cool if the blue Basculins had something to differentiate them further from the red.
Tall Girafarig. This is mostly 'cuz I just want Pokémon's one and only giraffe to get some love at all, but it was in the Sinnoh dex proper! The original one, even! It'd be cool if it joined Stantler in the new evo crowd.
Regional Mandibuzz? I know clashing exclusives aren't guaranteed to get regional forms (Meowth has had two new regional families while Mankey has gotten nothing) but it'd be nice if the vulture girl got a regional counterpart like Braviary. Her general design's already a pretty good fit for the region.