Expanding on this further: airports without a designated FBO could simply have a post with a (weatherproof) logbook on it and a simple park bench to act as the meeting spot.
The flight request would be for any aircraft on the ground (I could be convinced this could be available to any aircraft within 5 miles, almost like a MULTICOM thing). A person has the option to accept, decline, or offer a different idea.
When both parties have accepted, it puts you in a group with special tags that can be seen in flight, but also disabled. Up to 8, 12, whatever can join.
The ability to start right in the FBO would be an option, with aircraft and world-map planning to be selected later. If you are the first to offer and others accept your plan, you become the “leader” and their flight plan merges with yours and that becomes sticky to anybody who joins the flight, merging everybody’s plan with yours (independent of the aircraft you choose). If the leader drops connection, it goes to the next one who accepted, but the flight plan remains the same unless it’s modified by whoever is leading. “Updated flight plan, view?” Accept, decline. Then view it, accept, decline. Always an option to leave the group. Always an option to not participate in that aspect, but still interact with the other “static” FBO offerings.
Just spitballing. Hope it’s not inappropriate to the thread.