It would be useful to have a course waitlist or future (yet to be determined) session waitlist as well as a normal session waitlist.
For example, we have a popular course, we don't know when we will be running a future session, partly because we don't know how popular it will be. We'd like to gauge popularity by adding a course waitlist i.e. put me down for any future session you may be running.
We could add a new session, in a year's time with a max class size of 0 and min class size of 0 with a waitlist switched on but its not perfect.