Serious question, what if they just ignore the Forum and do it anyways?
At Worse: Get sued for breaking NDA, lose, pay a metric fuck ton in damages, and get kicked out of the forum and can never support HDMI products going forward.
But yeah even if the patch some how was made public, and it wasn't nuked out of orbit, ongoing support and bug fixes would be a pain in the ass. (Because as an example, no one from AMD would be allowed to touch the "patch code")
<edit> If AMD's planned patch was leaked for example, as AMD had not officially released it, its not yet "open source" and because of that, not yet public, and I'm sure there will be a clause in the terms that state that AMD would have to go on the offensive to get their code removed from any public repos. </edit>
When it comes to lawfare, The Forum wouldn't even have to be in the right (in a legal sense), just have a big enough war chest to make everyone else's life a pain in the ass!
The patent pools around approximately all the codecs used for media delivery are heavily cross-licensed. That includes HDMI and HDCP, but also h.264 and h.265. Most likely AMD can't legally use hardware decoding or encoding of any popular codecs at that point. Good luck with game video, streaming, or playing media discs.
So it would cost AMD - for example - their entire PlayStation/XBox business. At a minimum.
Probably makes it tricky to get HDMI forum's blessing for any future devices. AFAIK, the hdmi standards are public-ish so anybody can create a device that is HDMI compatible but you're only allowed to put "HDMI" on the packaging / marketing material with the forum's blessing.
Flipper × Raspberry Pi did exactly that just a couple days ago: https://blog.flipper.net/introducing-video-game-module-power...
> Video Out port: DVI-D signal in 640х480 px, 60 Hz. The port supports a well-known video standard that we can't name due to copyright limitations :shush: The first letter is H, and the last one is I.