Hi Roi! Your scubadiving forum looks really neat! Can you tell us some more about what you are seeking to do? You want to show events in public topics (to not logged in visitors) but limit who can see who has RSVP’ed to those events? Who should be allowed to see who has RVSP’ed?
We do have precedent for limiting privileges and access to things by group. I’m not sure if or when this feature could be implemented for the events plugin, unless more people ask for it and we are able to fit in the work.