When it comes down to how much he can capitalize upon the work he did with WotC/Hasbro in his new ventures there are three concerns: Copyright/IP concerns, contractual concerns, and quality of life concerns.
Absent the other concerns, Copyright/IP is easily maneuvered around for game mechanics. He likely is already well versed in this and has enough friends in WotC that he can avoid these issues pretty easily.
His contract with WotC might provide more of a barrier and might specifically call out things he can't do - and any severance he received may have been contingent on certain terms. You can fight these agreements in certain circumstances, but it is a pain ... and a fight.
Which brings me to the third issue: Quality of life. Fighting a corporation sucks. It isn't logical. Harrassment is often a technique. They can be big jerks ... so even if you're in the right, you can pay a higher quality of life cost by fighting them than just giving in when they're not pushing you too hard. To that end, I believe he'll want to be cautious and not risk angering WotC/Hasbro.
I wish him well. I hope that he enjoys being more free to do his own thing. However, with the upcoming Rules Wars coming as people fight between One D&D, Pathfinder, Daggerheart, Tales of the Valiant, and other contenders ... it may be hard to carve a place. Even with his name brand recognition, the split between systems will mean less money out there to support each of the systems, so whereever he hangs his hat, he'll be competing with established names that will be suffering from decreasing support as some of the people currently supporting their D&D Patreon go to others that are doing Daggerheart or Tales of the Valiant content.