In the UK “proper” ATC does not work for events like this. We used to have the biggest flyin in Europe – the PFA rally. One year the CAA mandated full ATC and imposed an order of magnitude increase in complicity including the “Lullington hold”. This was to go gone in history - songs were written about it! It is said that you can still hear the pitiful radio calls from people who had been going round and round forever. By late morning of the first day the ATC people walked out and the pilots just got on with it. The result was a very successful event with minimal incidents!
Rod1