I suppose your solution makes sense (although I'm sure the logistics of that would be a nightmare for the AO3 staff), but then you're back to an instance where wealthier fans are getting a perk that's meant to be for everyone regardless of financial status, which again, is not something the OTW wants to do, nor is it something that was ever promised.
Asking people to sign up in a queue regardless of their membership status has nothing to do with whether or not we "could make it work - if you just wanted to." It has to do with being fair and unbiased toward everyone in fandom, regardless of their financial means. I get that you're worried the sign-ups will happen at a time when some part of the world is asleep, and yes, that's always a possibility, but I'm sure the AO3 committees will do their best to be accommodating to everyone.
Honestly? I think you're worrying for no reason -- you might or might not get an account right away, but you will get one, so why all the stress?