WTR (and many others) would like to have a Track only be accessible to a set group of folks, and only have registration for a set window, since they are trying to run cohorts. For example, they want to run a Film Club and have everyone participate synchronously. So there would be a set time period when people can join, then the track closes to new people. They also want to restrict who can join, which the Paid Tracks might take care of now.