I agree with this in spirit, but market forces have proven that alternate reality titles are a hard sell. Not impossible, as books like Spider-Gwen, the Ultimate line (for a while) and Earth-2 (before Robinson left) prove. But it isnt easy, especially in a market where even books that are connected to the main line get cancelled because they're seen as "not important."
Now, if you just want to say there's a pre-Crisis earth out there somewhere and all those characters are still going strong....maybe have them show up once in a while in another book, like the old JLA/JSA annual crossovers....that'd be one thing. And I'd dearly like to see it. But as a stand-alone ongoing I dont think it'd fly.
Alternatively, DC could publish a title that explores the multiverse from the perspective of one of the main line guys. Vibe for instance, is perfectly suited for this. He's not a great example considering his last series fell flat but you get the idea. Have him travel the multiverse as part of his "interdimensional border cop" thing and let him run across those other worlds.
Something along those lines might manage to stay afloat for a while, if not Vibe in particular.