The problem is balancing on that.I think a very plausible contest idea would be to create a popfile for one of the existing mvm maps. It would be easy to test, and easy for people who don't even map to participate in, whilst drawing attention to what I'm hearing is the most difficult part of balancing an MvM map. Obviously we've just had an MvM contest, so we wouldn't get this for a while, but it would be an enjoyable change from the norm a little down the line.
A wave might feel intense for a bad team but calm and boring for a good team. And to restrict it to advanced could be a bad idea as many arent able to test with a team. While advanced is the mode that usualy has the more interesting waves.
Personaly i even would aim for expert normaly.
And then there is also the problem that some would just start with 5k cash and make it wave 666 style and some make it regular. Let some prefer a wave 666 and some prefer a normal style for gameplay. Someone who doesnt like a wave 666 style wave for that reason most likely wont vote for it, while it could be the better one.
It should have strict rules to balance on that, and with that the contest also becomes less interesting. So to me having another mvm contest on its own would be better. Obviously, the mapper should be allowed to ask others to make a popfile... after all, the only good way is if you can host a server and gather a team. And that isnt reachable for everyone.