Just a thought about the ultimate direction of the DCU once the consequences of Rebirth are sorted out: What if it results in a sort of "everything is canon" policy? We see Wonder Woman and Batman/Catwoman remembering fragments of their earlier incarnations' histories rather than their own, so what if Johns ultimately tells the writers to run with that? The heroes will become aware that they currently inhabit version 6.0 of their universe, and each of them remembers all the adventures that their Earth-Two/Earth-One/post-CoIE/post-ZH/post-IC predecessors had.
For example, Bruce Wayne will remember his parents' murderer never being found, but he will also remember Joe Chill being responsible. To the characters, it will effectively be like DC has had one continuous universe since 1935, even though it hasn't. And the best thing is that it doesn't constrict the writers afterward. Unless someone wants to retell exactly the same story, the characters having this knowledge wouldn't impact their future adventures beyond the writers' willingness to bring it up.