FC not useful outside XP buff.. gardening not worth your time, discord does better as social platform.
One thing I am sure of.. SE avoiding competition at any content. I doubt they will include any competition other than current PvP content.

About you suggestion:

-24v24 / 36v36 unlikely I never see 24 / 36 people online in same time at any FC.
-I doubt anyone will join faction war with crafter or gatherer . Crafting is a necessity for gil IMO not considering it fun.

I do have some ideas but... probably waste of time to write all of it SE have a static template and its unlikely they change anything from this template.