Hi Joy,
That’s a really awesome question and I know it’s something we’ve not only seen come up before, but also happens to be a pretty popular feature request.
While we haven’t started working on that specific feature, there is a way to use Event Tickets so that you can begin taking RSVPs instead of selling tickets once an event has sold out. And, if RSVP isn’t the exact word you’re going for, it would be fairly easy to change it to something else, like Waitlist.
Does this help answer your question? Please let me know. 🙂
Cheers!
Geoff