> not only is there no catch right now, but they literally can never add one. The SRD is released under CC-BY-4.0.

They can't change that particular SRD, but material not in the SRD can be changed as can new material. Also, as they leave the old OGL intact, it is a catch in itself: 1) It's generally restricts rights much more than grants them [0], and 2) WotC believes they can revoke it at any time.