I like this idea a lot!
1) 4 player fc's would get the same amount of subs as now, solo fcs would get less and bigger fcs would get more. Seems fair.
2) Players would be rewarded according to the amount of effort they put in, including both the leveling/equipment process and the daily logins to run the missions.
3) An fc leader couldn't reap the benefits of something others built, unless they donated it voluntarily.
4) Sublords would be able to operate all their subs within one fc and one house. Buying more houses would be an unnecessary cost.
5) Ownership of submarines could not be transferred to another character, which would make the resale value of a house be based solely on its location.
6) This would bring more fc members to the fc house on a regular basis and increase social interaction.
7) People would have a gameplay reason to belong to an fc. Buffs you can't choose, a bank you can't use and a house you can't decorate are not it, but a workshop would be useful to everyone.
There should also be a way to save submarine progress in those cases where a player leaves or gets kicked and joins another fc.