And my insane preference is a merged single Earth with a new history that has Jay as a part of the 1940's JSA alongside with those introduced in Legends of Tomorrow and maybe have them stuck in some Ragnarok pocket dimension so that Infinity Inc (made up of some of the wasted characters like Atom Smasher) could fill the void in the 80's and then have Tyler Hoechlin's Superman emerge in the 00's (giving him the same history as Tom Welling's Clark Kent). Then Jay can emerge in present day with limited powers to serve as Barry's mentor.
Because of December's Crisis, I feel like going light on the Big Bad may be a smart idea. Actually, assuming Bloodwork will be around all season, they could have waited to introduce him in January.