So, here's a proposition. Batman and Superman are never DC characters. Instead, they and their collective catalogues / families / rogues galleries are with a separate publisher (take your pick of All American, Entertaining Comics, National Periodical or a very early Vertigo), with all the related Golden Age and Silver Age writers. Meanwhile, this ATL DC Comics pushes and promotes the likes of Green Lantern, The Flash and Wonder Woman as their premier characters.
What are the repercussions?
Well, the big one I can spot immediately is that without Batman and Superman's mega-selling numbers, DC might never actually kick off the Silver Age and reinvent their other characters. The drive back towards superheroes was partially in response to the Comic Code yes, but without the basis of having two of the best selling franchises they might try to diversify their product.
Next, if they do actually kick off the Silver Age, then there's the immediate issue of Atlas / Marvel / Timely. DC executives took Marvel lightly for years because they were still outselling them, but people inside the company who were keen-eyed knew that was because characters like Batman and Superman were killing it at a time and were actually subsidizing a lot of badly selling titles. Without those characters or supporting elements like the Legion, DC is actually going to have to be more cognizant of the threat Marvel poses much earlier, though given their OTL planning, that might not amount too much.
In discussing the Golden Age, we can't forget the likes of Earth-1 and Earth-2. While Earth-2 promoted and protected all of DC's Golden age iterations, without Batman and Superman around Earth-2 might actually diverge much more than it does IRL, with the likes of Alan Scott, Jay Garrick and other Golden Age characters actually getting sustained presences without GA Batman and Superman hogging the picture time. Or maybe this Silver Age just reboots all their characters, so we don't have Hal Jordans and Barry Allens at all, just their reboot versions.
If we try and peek way forward in time, Superman and Batman's film success in the 1970s, 1980s and 1990s is definitely gonna provoke DC to try and compete earlier. Maybe they try and launch a Wonder Woman film in the 1990s, maybe that Flash tv show gets more than one season? Animation is sure to be a lot different as well, with Batman / Superman shows competing against Super Friends (or whatever DC calls their lineup).
And of course, there's gonna be a lot of continuity changes. No Robins in the Titans, for example. The Justice League needs two founding members (Black Canary and Green Arrow?). Captain Marvel won't be a DC property. Martian Manhunter's look and backstory might change to avoid that same fate. And so on and so forth...
Any ideas, guys?