[trynewideas]

Then remove IP you want to protect from the CC BY-licensed SRD, publish the books under normal copyright terms, and add the rules content to the SRD?

I still don't understand the value of the OGL spelling out reserved IP. That's already protected if the only open-licensed part is the rules text, which (not a lawyer) happens with a CC BY SRD and any other copyright license on the derived works.

Wizards leaving reserved IP in their official SRD was a bug, not a feature. Back when Paizo still self-hosted Pathfinder 1E's SRD, they solicited pointers to and removed protected terms that they accidentally left in it so it'd be more ergonomic for publishers.