With the landscape as it is, I think the ideal scenario would be the solo in Keystone option. They could also keep him in Titans if he needs to be on a team. I think Barry's footing as the primarily Flash is about as strong as it can be with everything his character has going so I don't think a Wally solo would infringe on that in any significant way.
Allowing both Barry and older Wally to succeed just seems to make the most sense for everyone based on the decision to bring Wally back.