I see what you're doing, but I'll bite.
If WB didn't have Batman and Superman movie rights, I think they'd do what they've been doing. Watchmen, V For Vendetta, Green Lantern, Jonah Hex, Constantine. They just announced Sandman. More Vertigo-related titles. A History of Violence. Road to Perdition. RED. More adult-oriented material, because frankly, DC has more adult-oriented material and isn't bound by just superheroes. Really, not an amazing filmography, but they'd still put one or two out every year like they've been doing. Definitely more Vertigo stuff - Y: The Last Man, 100 Bullets, etc.
I'm not sure where the A-List stops with DC and the B-List begins, but I wouldn't put Wonder Woman, Flash, or Green Lantern on the B-list. So, nothing would be happening there. I'll admit that Batman and Superman are ultimately DC's bread and butter. But it's the same case with Spider-Man and X-Men with Marvel. The only difference is, we're talking in hypotheticals; DC actually CAN (and will) put them all together.
Marvel, for example, has second-tier characters, (and third-tier, and fourth-tier). Nobody knew who Iron Man was in 2007, and they turned that around in one year. I applaud them for that.

Same with Thor. Nobody gave a damn about Thor. These Avengers characters (I'll include Ant-Man and Guardians) were like the comic books our moms picked up for us at the grocery store as a surprise, because the comics were in a bargain bin for 99 cents, and we threw them in a corner because we suddenly realized our moms were poor and couldn't afford X-Men for us.
By the way, this is a more suitable topic if the question was,
"What if DC Comics started a movie studio called DC Studios, but they didn't have the movie rights to Batman, Superman, Wonder Woman, Flash, and Green Lantern?" And,
"DC Studios only has the movie rights to Hawkman, Red Tornado, Metamorpho, Cyborg, and Zatanna."
If Marvel had the rights to all their characters, it would be a DISASTER. And the reason for that is that they have three-times as many characters as DC does, and that's not a good thing. Again, quantity does not equal quality. If Marvel seriously explored the idea of putting Spider-Man, X-Men, Fantastic Four, Iron Man, Hulk, Thor, Captain America, ALL IN ONE MOVIE, it would be an absolute disaster. You thought Spider-Man 3 and X-Men 3 was a problem? Oh boy, you couldn't imagine.
In my opinion, I LOVE that Marvel Studios doesn't have Spider-Man, X-Men or Fantastic Four. It puts them in check. I don't like shared cinematic universes all that much. I think it ends up being limiting instead of making it more expansive. Instead of opening up infinite doors and infinite possibilities, it puts everything in a corner. It does the opposite of what it should do. I'll go on record and say that I don't want WB toying around with Justice League for too long. I basically want:
Man of Steel
Batman vs. Superman
Justice League
Wonder Woman
The Flash
^ And that's it. That's all I want. If Justice League 2 is thrown in there, along with Solo Batfleck, that's fine too. But not this craziness that Marvel's doing. Let it end at some point.