Would not mind that ability to join more FC's than just 1...
Maybe like 3 or something like that, it would be a nice addition to stuff and you would only be able to master of one of course and the main one you are in or first listed would be the only one where you can tamper with FC stuff of course, workshop/subs/ships/decoration etc..
Just a suggestion to maybe be able to spread out the more social thing about this game at a wider scale.
Sooooooo linkshells?
The problem is clearly that they made the workshop/sub/ship stuff tied to an FC. It causes people to go and make their own exclusive FC, with just them in it, to do the content.
Aside from that, the way you have multiple "FCs" in this game is through linkshells and Cross-World Linkshells. Mostly the same thing - a chat.
Guild Wars 2 was nice since they allowed you to join up to 5 guilds.
Even if the limit were as low as 2, I'd quite like this - since I'd be able to join an FC without being forced to lose my now-unsubbed friend group's FC along with our house and workshop progress. It gets lonely being the only one left.