As it was described to me, the watermarking is encoded in such a way that it would be prohibitively expensive computationally to offset or overwrite it.

Okay, let's assume that's remotely possible. Injecting such a watermark at the camera doesn't help you - in fact, such a watermark you're describing is attempting to be resistant to things like re-transcoding so it might actually be carried through an editing process successfully. Not to mention the previous camera sensor bypasses. So let's ignore camera based options.

You have to get all video editing software or displays to inject such a watermark while keeping their keys private. Getting direct LVDS access to a panel and being able to write your own firmware pretty much bypasses most display options, and well... software based options are even worse I'd say, software is open to such a wide array of attacks and the mere existence of open source video editing tools, including FaceSwap itself makes this seem... questionable at best.