We have started with FEP-8485 Unbound Actor, aiming at a ValueFlows based relationship between any kind of actors.
And this was discussed, re-thought, re-designed, and went through various iterations on SocialHub Thread Decentralised Group.
It wasn't until we had finished implementing the federation of Groups, polishing our Notification system, and defined how we wanted to represent all of this internally for GNU social v3, that we fresh started with all these ideas in mind and came with the simpler FEP-2100 Unbound Group and Organization.
Which instead builds on top of the already existing logic for Following. Of course, this FEP assumes how GNU social (and Lemmy, Friendrica, and Lotide) understands groups (and organisations). But we believe that, now that implementations are using these ideas and strategies, after a few more testing time, everything should become reasonably specified and formalized. Being this FEP already a step and contribution in that direction.
This FEP was implemented in GS via a plugin.