I don’t know exactly how they will portray Ben’s redemption, but I definitely see it happening, and I think Rey will play a part of it. I think it will be romantic love that puts the galaxy back together.
It’s a theory I’ve heard often (even literally my mom said this was her theory after she saw TLJ) and while I don’t have anything against it, personally I’d be surprised if it happens in an explicit “Rey and Ben are a romantic pair and will live happily ever after” way.