I would have ended it with a small handful of existing parallel worlds: Earth-2 (with the JSA who started in WW II), Earth-1 (but let them all be a little older), Earth-S for the Captain Marvel characters/milieu, and maybe a Milestone Earth. And then a new Earth-0 on which they could start a new continuity, without all the clutter, baggage, and duplication we got in the post-CoIE DCU.
And I would have had limited contact between those Earths, and added new Earths very slowly.
On Earth-0 I would not have had Diana debut as Wonder Woman years after Superman and Batman started out. I would have kept her as a founding member of the JLA, and kept a strong, sisterly relationship between her and Donna.
I realize this is not precisely an answer to the question asked - but it's close, and it's what I would have liked to see.