After having given it some thought, the only way I would accept Hisuian alt evolutions for Cyndaquil, Rowlet, and Oshawott (which, BTW, hasn't happened yet (Alt Regional Evolutions have so far only been for Regional Variants) so that would be a new precedent if it did) is if it was done via some artificial way. As I said, the original reason I've pushed back is because REGIONAL Variants means that Pokemon is from that region and has adapted to it; it's specifically said that the Cyndaquil, Rowlet, and Oshawott Starters are foreign Pokemon brought to Hisui by the Professor. It won't make sense for them to have a natural Regional Variant.
So, if they were to have one, I'm expecting maybe at some point player & Starter will be exposed to ~something~ (likely Arceus-related) and, while nothing happens at that moment, the Starter's evolution course has been changed. NOW, the question is when this ~something~ happens:
- Will it be early one before the Starter evolves so that starting from the middle stage they've been given special Regional Forms?
- Or, since they've been "hiding" the evos, would they first try to psyche us out (ha, yeah right, like a misdirection has stopped speculation before) by revealing the mid stages are the same but that's when they're exposed and have a different final stage.
I supposed there's a possibility they'll do a second psyche out, revealing all evolutions are the same... EXCEPT the final stages have a special Battle Bond trait to them and they have Battle Bond forms (notably all of the Starters are from Starter Groups who don't have a super mechanic like Mega (like Kanto & Hoenn), Gigantamax (Galar), or another Battle Bond (Kalos); giving the (generally) most popular members of the groups lacking a super mechanic (Johto, Unova, & Alola) something like Battle Bond could be GF's way of giving each Starter group something special even if not all Starters within that group have it, but that's another argument for another day).
As for WHAT they could become... I'm not even going to fathom a guess. If what I'm predicting is true, then honestly exposing them to "god energy" means they can become ANYTHING. Will they become more humanoid? Will they become more to resemble the symbolism why those three were chosen (representing weapons of that era: black powder/fire, swords, and archery)? Will they change to resemble mythical creatures taking on design aspects of Arceus/the Timespace dragons? I'm just gonna wait and see. I'm personally still curious if Wyrdeer and Basculegion is a new cross gen evolution or they're going to reveal H-Stantler and H-Basculin revealing their Regional Evolutions.