Sandman is Neil Gaiman's most cherished work, I would assume. I feel like it is definitely something he wants a lot of control over. 100% control? I'm not sure. It's still a DC property, but we'll have to wait and see.Expected, but unfortunate nonetheless.
I have the same head-canon.Random opinion (admist some dead air): I'd like to think Gotham is set on Supergirl's Earth (Earth-38). Gotham being the "darkness" of Supergirl's "light" world.
One timeless and (somewhat) 'grounded', one contemporary and 'fantastical'. Two parallels representing opposite symbols - fear and hope.
Obviously it can't be set on Earth-1 because of the different Nyssas and Cyrus Golds, Nora Fries being dead in Gotham, etc. Although, I think the idea of Gotham taking place in Earth-38's past would condense things slightly, since Supergirl's Earth already has its own Batman who we still know nothing about. Gotham (the show) could fill that hole, while Batwoman fills the hole of Earth-1's Batman story.