Waitlist for full meetings

Is your feature request related to a problem? Please describe.
The City of Zürich has started to use meeting registrations quite extensively. One problem we encounter is that there currently is no way to manage a waitlist. This is done externally, causing chaos with registrations and cancellations via the platform and also through direct contact with the project organizers.

Describe the solution you'd like
We propose expanding meeting registrations with the functionality of having a waitlist. This would work as follows: If activated and a meeting's slots are entirely full, I can click a button "Add to waitlist". I would have to provide the same data as required by the registration form. Now, if new slots become available, Decidim will automatically (based on first in-first out) transfer people from the waiting list to an available slot, notifying the user that he/she is registered.

Describe alternatives you've considered
Alternatively, providing details of the registration form could only happen when a slot becomes available. This may be better from a GDPR standpoint as less data is collected overall, but involves one more step where the user has to become active. This would also require designing a solution for what happens when a user is allocated a slot but fails to provide the details required by the form.

Does this issue could impact on users private data?
Not more than with the current registration, details in the point above.

Funded by
possibly by the City of Zürich