@Ruin Explorer
Paizo has been publishing a commercial competitor to D&D for nearly 15 years now. They were never going to sign a licence along the lines of the OGL v 1.1, given that it requires them to give up almost all of their existing business.
And WotC must have known that.
Much the same is true for various OSRers, though I don't think any of them are on Paizo's scale.
I don't know about the 5e-supporting 3PPs. But given that WotC's goal was to regain control of their IP, I don't see that they are failing in that goal when all their licensees give up their licences.
Again, I am not saying anything about whether this serves WotC's longer-term commercial interests.
As far as publishers defending the existing licences in court, I can't believe that WotC hasn't anticipated that possibility. It's such an obvious one. What I'm curious about is what advice WotC have had in that respect - as per my exchange with
@S'mon not far upthread, I'm one of those who thinks the better legal view is that WotC cannot unilaterally bring its existing licence agreements under the terms of the OGL v 1.0/1.0a t an end.