If there isn't an expectation of being vaccinated to attend (even just a checkmark "I have been vaccinated" without any proof required), it will likely be replaced with some giant pile of legalese that covers their... behinds thoroughly, both for those who may attend despite an unvaccinated status, and for anyone with a medical condition that would make contracting Covid particularly dangerous.
Yes, at some point society will go on with something resembling normalcy, but even with the leaps and bounds of improvement the US has seen in reducing its numbers, they're not low enough yet (or, the vaccination rate isn't high enough yet) that the idea of just winging it is sensible, not as an attendee and especially not as an organizer.
People should actively want to get a shot before entering a space with thousands of strangers, even if the reality is that there are some people who for whatever reason hesitant (in the US, sadly political ones) or are willing to risk their health and wellbeing to attend the event.
At some point Gencon LLC isn't required to protect people from themselves, and I imagine the policies and procedures will be guided by science to protect the community, and also their Legal representation's efforts to ensure that due diligence is done, i's dotted, t's crossed, etc.
Note that I state this conversationally, without judgement or derogatory tone. It's a reality of the world we live in, prior to Covid, and a company running events of this size would be insane not to have those considerations in place.
We, as potential attendees, need to be cognizant of such things, and respect that some of the choices may indeed be beneficial all around, others may simply be the medical equivalent of 'security theater' or "why we took off our shoes at airports for like a decade because". Nod, smile, accept it for what it is and don't make the day any tougher on the poor soul enforcing the policy.
Which, hopefully won't be something the staff have to deal with much over the weekend, but it'd also be absurd to expect tens of thousands of people to attend and not have someone lose their cool over being asked to mask up or sanitize their hands for the Nth time that day, or whatever the trigger point might be. Or getting called out on one of those 'I don't have to wear a mask, see I laminated my own card and everything' types.
Let's all strive to not be 'that guy/gal', because some will fail at that goal.