You appear pretty certain where one class tournament may or may not be held. Since no decision has been made to do it, it certainly has not been determined that it would have to be at a school and not an arena.
Hays is very succesful with one tournament for lots of reasons but right at the top of the list is because the public turnout for the event is simply overwhelming. Frankly, I think 4A could do the same thing quite easily. As for the ability to do it a high school, I have little doubt that a facility like Basehor-Linwood could easily host a 4A state tournament. Not that it would be a top contender because of the extreme location.