It’s hard to say because he just caught Galarian Farfeche’d but if I had to put some money on it, I’d say Galarian slowpoke because of the new Isle of Armor. Maybe a galarian darumaka to counter Goh!
As for alolan forms, I’m pretty confident that he’s not going to catch any Alolan Pokémon in general because his team from that region is pretty settled imo and there’s not many options for him to improve his team with.
Alolan Sandslash, Exeggutor and Passimian are the only Pokémon from that region I think would suit Ash and make sense story wise. Alolan water types were either kind of lackluster or already belonged to someone else, Bruxish would’ve been interesting because it was also part psychic type but no..
He had 2 bonding episodes with Exeggutor and Passimian, so he could’ve caught them.. And before Melmetal existed there was a lot of speculation that he would catch Alolan Sandslash because he did need a second ice type Pokémon on his team!
Kommo-o is a nice, but Ash already has the much rarer Naganadel as a dragon type and I don’t think he needs another pseudo-legendary or a fighting type considering he already has Dragonite and Riolu to fill those roles.
If they wanted him to catch those Pokémon, they would’ve taken that chance in the last series.. When Poipole was released, they had over 50 episodes before the Alola League for Ash to catch a new Pokémon or 2 and he didn’t, so I don’t think they’ll open that door up again.
I guess the writers were satisfied with Rowlet, Lycanroc, Incineroar, Naganadel and Melmetal in terms of rarity and typing. Considering he was going to school and having fun for most of the series, that was a pretty nice team he ended up with!