We use Pro and Community to list events (and have members list events) going on in our niche. In Community you can require users to be logged in as members in order to add events, and members can see the events they’ve added. It seems a natural extension to Community would be to allow those same logged in members to RSVP to events.
I would envision a section that simply says “Going? Yes – No – Maybe” that logs members responses. It can create an additional view “Attending Events” similar to the “My Events” view, but instead of showing events added by the member, it shows events RSVP’d to by the member.
Bonus: function that returns all the user IDs of members who responded with either Yes, No, or Maybe to a given event.
Could something like this get developed for Community or Pro? It seems like it would be a natural extension to Community that would make The Events Calendar even more appealing as an event solution.
Note: I’ve also added this as a feature request in your UserVoice forum, but wanted to make sure it was posted as well in a paid-member forum.