Even if they released an unrevocable version of OGL 1.0a, at this point there's a pretty high chance that 3PPs would use it as a base for a 5e continuation instead of supporting WotCs vision of the game. They regained trust once with 5e using the OGL again, but 3PPs would be foolish to trust...
Onyx Path have issued a statement in their Monday Meeting Notes:
http://theonyxpath.com/old-grey-labrador-monday-meeting-notes/
Pugmire will move away from the OGL and use its own system and license (they explain it in more detail, but I didn't want to copy the whole page.
The idea of a library...
I'm currently checking the Pathfinder 2 PDFs I got a while ago through Humble Bundles. And then there's Exalted, Trinity, Scion, CofD, They came from ..., Shadowrun, Earthdawn, Midgard and several other systems.
There's also Midgard (not the Kobold Press one), but it's currently only available in German. It's rules are somewhat similar to d20, but have been used since the 80s.