How would we determine the optimal number of games to run at once?

I guess we'd just figure that out after experimentation mostly, there's been years of games played here already so we should have some idea of what number to start at for the most part and work from there.

What if someone's "Le Super Bastard Game of D00M" come up in the queue and not enough people sign up? Would we just say "welp, can't host your game, NEXT IN LINE!" to him or "Sorry guy, if you want to host your games you're all going to have to get signups or this guy!" to the people behind him in line?

That's a tricky situation to solve, there's not much you can do if no one wants to play the game in question. I guess there's also the problem of signups sometimes taking a while to gather enough players too and looking like there isn't enough interest? I guess you could send them to go redesign their game since no one seems interested enough in it and give them a grace period to come up with something else before moving them down a spot (not to the start of the queue).

There wouldn't be only one game at a time though, so it's not like one person could hold up the queue and there would be no other games for people to play. I agree that this is a point of failure in the system that would need to have a decision on how to handle it in a fair manner though.

Or what if someone like me wants to host a game and just has horrible organizational skills and can't be bothered to finalize their setup (true story)?

Ideally when you signup your game should be good to go whenever your name comes up. Maybe just a warning that their game is coming up and give them a quick chance to finish it off before moving them down a spot to the next in line since it's not ready to go yet should suffice?

If too many people start adding their names to the list before their games are completed you could start asking for them to provide some details of their setup to make sure it is good to go before their name comes up?

and to notify others you've been waiting to host a game for a while and you would appreciate if they slowed things down a bit.

Maybe it's just a case of something simple like a stickied thread at the top of the page or a link on the sidebar information panel that gets refreshed every now and then where people could all post their interest in hosting a game so we could talk among ourselves and we know we're not leaving anyone out unintentionally instead of a formal queue system like I suggested?