Kha'Zix I find extremely unlikely get a PROJECT skin, because he already has a Mecha one, which is already very similar to PROJECT. Same goes to Irelia (for her Infiltrator skin), Akali (who has Silverfang and Headhunter skins), and Miss Fortune (for her Gun Goddess skin/looking to much like the other marksmen in the skinline, namely Lucian), although I still find them more likely than Kha'Zix.
Even though he has a Hextech skin, it could work for Alistar to get a PROJECT skin, but generally the PROJECT skin lineup is made up of assassins/marksmen, and not a lot of tanky Champions. So my bets are on Alistar to get another sci-fi skin other than PROJECT, maybe Mecha.
Nocturne is an interesting one. I definitely think they could make it work as long as it doesn't end up looking like Eternum Nocturne, but at the same time I feel like PROJECT isn't exactly his skinline. Maybe Riot will end up giving him a Program one. I don't quite know.
I would like to say Riven is a top pick for this skinline, especially with her lore and theme as an exile, but again, she doesn't fit the general lineup of marksmen/assassins. But who knows? Maybe they'll make an exception for her like they did Fiora and Vi.
Overall, my biggest predictions in this particular group of Champions getting a PROJECT skin are Talon, Diana, and Evelynn, as all of them do not have a sci-fi/technology-based skin already, and could fit into the skinline pretty well. And out of those three, my vote goes to Diana for fitting the PROJECT theme the best.