The FAQ says the waitlist is ordered, only the initial sign-up period was unordered.
What if I don't sign up before September 17th at 10 a.m. Pacific?
After the one-time randomization at that time, anyone who signs up will be automatically added to the back of the waitlist.
I received an email that I'm on the waitlist, what does that mean?
It means that when we did the one-time randomization of the reservation queue, your place in line ended up beyond the number of Steam Frame units available to reserve. As we work our way through the queue, some customers may cancel their reservations. If that happens, you may be moved up in the reservation queue, and you'll be notified via email that you have a reservation after all. But if not, nothing about your position in the waitlist changes, and any future production runs of Steam Frames will be offered to customers in the order they're on the waitlist.