With Cavalier, Witch and Warpriest in, I think the following new classes are the most likely for further inclusion aside from the Alternate Classes: Arcanist, Bloodrager, Hunter, Skald, and maybe Mesmerist and Investigator. Arcanist, Bloodrager, Skald and Hunter all use recycled or simple to implement class features, in fact every single one has been implemented in a mod for Kingmaker. Mesmerist and Investigator have one small that's easily addressed.
Mesmerist would actually be fairly easy to do in turn based, but its dependence on activating its main ability out of turn hurts it. Still, it's doable by giving painful stare a slightly different implementation by making it a toggle and letting them get the d6 bonus damage (but not the initial half mesmerist or any riders they have) if they hit with an AoO after an ally has already hit the enemy and triggered painful stare that turn. As far as I know there's nothing in the game that cares about how much damage you deal in one hit (aside from DR, which painful stare already requires you deal enough damage to beat DR to use it) so the difference would be minimal. Investigator's signature ability is adding bonuses to out of combat skills a few times per day when you want to, but is doable with minimal issue by an official implementation (include a UI thingy in the dialog interface that selects using inspiration for the next picked check).
As for why I didn't include the others... The other psychic classes classes have lots of weird rules that wouldn't work in a video game or (in the case of psychic) are just a shittier sorcerer nobody wants to play as. Brawler can pull out any combat feat in the game on demand, which would choke flow for little gain (you don't have feats that are nearly as situational). Shaman is a design clusterfuck that without the ability to shift class features every rest is just a shittier Witch.. Swashbuckler and Gunslinger, in addition to being horrible/meh respectively, depend on GM fiat for the panache/grit pool. Summoner depends on adding extra limbs to a creature, which is a horrible mess in a game with non-abstract graphics (Knights of the Chalice 2 could probably get away with it).