Finn
Since Rey and Kylo Ren are both getting inserted into Star Wars Battlefront II, there’s definitely no boundaries restricted to other members of the New Trilogy as well. No character from that trilogy lends themselves better to a game covering multiple eras quite like The Force Awakens’ Finn. The trooper formerly known as FN-2187 has a large fan community following him (of course he does, look at the universe he’s in), and John Boyega himself is a huge fan of the series, even advocating for a single-player mode himself back when the 2015 game was lambasted for omitting.
Now that this new game will have a single-player mode covering multiple eras, there’s potential for multiple perspectives to be covered in the game, a la Battlefield 1. Finn’s story is going to be covered in future films, and that’s totally fine. But, he was in a squad of other Troopers who he grew up and fought beside. Even though we all know the grim fate that awaits them, it would be interesting to play as a Trooper alongside our favorite traitor–either FN-2003, who dies at the beginning of the film, or the infamous 2199.
As far as multiplayer’s concerned, we know that he’s quite handy with a blaster, and even though the films are being coy with this right now, there’s still a fairly good chance that he’s a Jedi. Don’t worry about the logic of him having a lightsaber, just give him Luke’s old one and let players do what he does best.