There are still 77 spots open for "new" Pokemon in the usum dex. Going off 10 Kanto Alolan form families there "should" be 10 Johto Alolan for families. I've put together a chart leaving the unused mons that could have Alolan Forms.

My guess for a top 10:
>Bellossom (Fire/Fairy, Grass/Fire)
>Noctowl (Ice/Flying, Psychic/Flying)
>Girafirig (Dark/Psychic, Normal/Ghost)
>Magcargo (Fire/Water, Water/Rock)
>Dunsparce (Fairy/Dragon, Posion/Dark)
>Ursaring (Dark/Fighting, Grass/Dark)
>Donphan (Water/Grass, Water/Steel)
>Octillery (Water/Fire, Steel/Fire)
>Sunflora (Grass/Fire, Fire/Fairy)
>Qwilfish (Water/Steel, Steel/Fire)

I feel like it makes sense for the remaining Pokemon to get Alolan Forms. Let's just hope gf delivers.