So Doomsday Clock #12 revealed that the New 52 era of comics has been preserved on a new world called Earth 52. How would you like to see DC handle this Earth?
Here's how I'd handle it:
The “breakpoint” is Superman Reborn; this fits the criteria for Doomsday Clock's “split off a new world to preserve an era of Superman”. But this change propagates back in time all the way to the start of the New 52. From the beginning of the second wave, things begin to change: no one from Earth 2 ever visited Earth 52; just Earth 0. So no World's Finest title, and the Earth 2 title never had much to do with the New 52 anyway. In and of itself, this isn't a major change; but it starts a snowball. For instance, Futures End doesn't involve refugees from Earth 2.
Mr. Terrific never meets Power Girl, and never leaves Earth-52. Tanya Spears never becomes Power Girl.
There's no Forever Evil for the same reason that there's no World's Finest: Earth 3 attacked Earth 0, not Earth 52.
Convergence also doesn't happen on Earth 52, meaning no appearance of a pre-Flashpoint Superman and no Titans Hunt. But most of the DCYou initiative continues apace — up to and including the Last Days of Superman. On the other hand, the follow-up series, Superwoman, doesn't get derailed by Superman Reborn. It also takes a somewhat different course, as Superwoman is the one who challenges Lex Luthor about replacing Superman.
Also, no Rebirth, for the same reason as the others: there are no extra-universal incursions onto Earth 52. Wonder Woman never learns that her origin is a lie (and on Earth 52, it isn't). Ray Palmer never gets stuck in the Microverse; Ryan Choi and Ted Kord remain dead. Some of the post-Rebirth stories might still happen, like Green Arrow Aquaman; but for the most part, they don't.
On the other hand: a very different kind of Superman Reborn ends up happening, as Superwoman discovers a way to bring Superman back to life — at the cost of her powers. Which, ironically, ends up saving her life, too.
But by this point, Earth 52 doesn't resemble Earth 0 at all.