Really disappointed that CCC's reason for cancellation has such an anti-vax undertone. They already scan QR codes for tickets and check wristbands at the door, how would scanning an vaccine QR code change the "Congress spirit"? https://events.ccc.de/2021/10/01/absage_praesenz_2021/
@th Restrictions might well include more than a vaccination requirement. People can still get infected when vaccinated (we recently experienced one such case at home, and baby's day care was closed for more than a week as a result). I would imagine strict segregation of the various conference spaces, food supply safety, distant seating during talks, distance between tables in hack rooms, emergency response in case of an outbreak, and more would need to be considered.
I think checking everyone's vaccine status is not sufficient if you want an event woth 14k people intermingling. Scanning the QR codes is not the problem. The problem is that it wouldn't be sufficient, and it'd be a recipe for disaster if you just pretended it was (like some festivals did this summer).
@th I was about to say "the limiting factor is how many sweaty hackers you can safely pack into c-base" but I guess it hasn't been in Berlin for a while.