That's what I see as being the deal breaker. Someone is going to disregard the rules, and when asked to follow them will become belligerent. That could end up as a lawsuit.
I think a lot of these things come down to whether you choose to see the glass as half-full or half-empty. You earlier posted that it was bad that only 22% of the public is vaccinated. Personally, I think that's good news -- headed in the right direction. Similarly, I think you are overly pessimistic about rules compliance.
I manage a public building that has had literally tens of thousands of people through the doors since the pandemic started -- including more then 26,000 just to vote (polling location -- so it was people of all political stripes). In all that time, only 1 person has refused to wear a mask. That person told staff he wouldn't do it. We had a supervisor repeatedly offer a mask and insist that he will have to wear it or leave. Ultimately, after some back and forth, he agreed to wear it, but told us how 'dumb' it was. My point is that I just don't buy that non-compliance is a big problem. People know what they have to do to go to Target, Home Depot or wherever. They may or may not like it, but they know what the deal is when they go there.
If you look on Youtube, you can find a few people getting arrested, so anything can happen. But, these events are extremely rare. Again, my building had tens of thousands of people and zero times we have had to call the police. I have no idea what the lawsuit is about that you are imagining coming out of this.
TLDR:
1) We don't even know what the rules would be yet
2) Virtually everyone WILL follow the rules (even if they don't like them) just like they do everywhere else right now
3) Gen Con would have a plan in place for how to respond if someone doesn't follow the rules
The glass is half full. And there are four lights.