But then again, we don't know what if any licensing terms are going to be available. Assuming they go with a GSL license--If the GSL has similar freedoms (no fee, no need for prior permission), except some extra requirements (for instance saying you can't reproduce the rules from the PHB in your work and you can't depict extreme depravity in your products), then you are then ignoring the legal license and making more of a challenge against WoTC in that case.
If there was no license whatsoever, then you might have more traction to stand on. But if there's a license available and you deliberately challenge it because you dislike the reasonable terms, I think that would be a lot harder to prove, since that sort of infers a more hostile intent.