Flash is doing pretty well for DC since Rebirth, in no small part thanks to the success of the TV series. Could it be possible for it to get a second ongoing? If Green Lantern can have two books, I don't see why The Flash can't.
I would love to see a Speed Force book focused on the Flash family (when they eventually return), a la Tynion's Detective Comics. Having Wally plus a lot other characters could help push the book.