bmfrosty
Adventurer
This happened already, but instead of licensing it to a single company, they've given anyone the chance of doing it through DM's Guild. I believe I've seen a Ravenloft Gazetteer floating around there some time ago, and the same could be done with Forgotten Realms, if people wanted to. In time, I expect some publisher to arise as the go-to third party resource for setting material released through DM's Guild, much like we learned to sort gold from garbage in rulebooks from the d20 era.
They're only allowing FR and Ravenloft on DM's guild for now. Eberron, Dragonlance, Greyhawk, Dark Sun, and Planescape are still not allowed.