Logically, Game Freak will cut the number down to either around the same amount of the original Alolan forms (18) or perhaps even fewer because fewer pok?mon originate in Johto.
To cut down to this number, I've tried to consider a variety of factors including the pok?mon's marketability, competitive usability (and competitive potential with a few changes) and finally I searched 'Alolan ____' into google images to see if any good concept art was available, if it wasn't then logically that pok?mon is either difficult to redesign or overlooked so much that there is little reason to make an alolan form for it.
- Sentret , Furret (Having already seen Rattata and Raticate receive Alolan forms, this seems like a logical inclusion. If GF is being lazy they can just make them dark like Rattata & Meowth, but hopefully a better idea would emerge)
- Hoothoot , Noctowl (I think there's a fair bit of potential here. A lot of reasonably good concept art seems to position Noctowl as an Ice type, I think it would be good as a pok?mon at Mount Lanakila. Noctowl is also well remembered as one of Ash's pok?mon from the anim? which swings in its favour. Perhaps Hoothoot could retain its regular form, but evolve into the Ice-type Noctowl when levelled at Mount Lanakila)
- Natu , Xatu (There is some fairly cool art on Google Images were Natu & Xatu look like disciples of Tapu Koko, perhaps four different Alolan forms for each Tapu would be cool.)
- Hoppip , Skiploom , Jumpluff (I think like quite a few pok?mon here, this evolution line is often forgotten about. There is some reasonably good concept art of a fire-type version of Hoppip & Jumpluff, but I don't think GF would go for this one.)
- Sunkern , Sunflora (This would probably be a difficult redesign, there is an issue in that sunflowers seem well adapted for Hawaii. The marketability of these pok?mon is also suspect, whilst any competitive viability would require a huge stat upgrade.)
- Wooper , Quagsire (I love these pok?mon and would love to see them given a bit of exposure, but fairly similar pok?mon in Barboach & Whiscash are already present in Alola. Perhaps Quagsire would not need to adapt.)
- Unown (I think GF would prefer to keep Unown as novelty pok?mon with little competitive viability, also a difficult redesign)
- Girafarig (There aren't many concepts for this available. It might be cool to see a Moon-exclusive were the dark back half consumes the front and it becomes a dark-type, but I would imagine Girafarig will get overlooked.)
- Pineco , Forretress (These two have only ever been in the Johto dex. You can either take that two ways - 1) They're overdue an inclusion in a new game. 2) GF has no interest in utilising these pok?mon. I'm tempted to go with the latter, but I wouldn't mind seeing them become electric similar to Geodude, Graveler & Golem.)
- Dunsparce (No chance.)
- Qwilfish (Probably also no chance, but I do like Qwilfish so that is a shame.)
- Shuckle (I love that Coconut Shuckle posted earlier in the thread. I do think Shuckle is one of the least likely of my inclusions to make it, but whatever it has a reasonable chance. It certainly isn't as horribly unpopular as Dunsparce or Qwilfish.)
- Teddiursa , Ursaring (These are the type of pok?mon Alolan forms should be used to revolutionise, regular normal types based on real-life creatures. Dark type makes sense following the original game, but if they could turn Teddiursa into an even cuter Fairy type that would be cool.)
- Slugma , Magcarco (There is some cool concept art of Desert Slugma, so perhaps a ground type of that in Haina desert would be cool. These two aren't particularly popular, but I feel like pok?mon of similar popularity (Numel, Camerupt) have been given special treatment in the past.)
- Remoraid , Octillery (I would like to see an Octillery which, in contrast to Corsola, blends in with the Alolan sea predator Toxapex and changes it colours to match it. A change of typing to water/poision and perhaps changing the effect of Octazooka to have a chance of inflicting poision when used by an Alolan form Octillery would be cool. The only issue with this is Remoraid's relationship with Mantine, so I'd be tempted to exclude it, but not Octillery.)
- Phanpy , Donphan (I'm not exactly sure how this line would adapt, but I think Phanpy and Donphan have great potential. Phanpy especially as a cute pok?mon. I'm sure the more imaginative folk at GF can work on it.)
- Stantler (Similar to Pineco, this pok?mon never makes it to foreign regional dex. I don't see that changing soon and Sawsbuck has already removed a lot of its potential options.)