Cooldown already exists for leaving and joining at 24 hours. It's already obnoxious enough when most games have a 2h cooldown so I'd rather not make it longer lol. Imagine meeting a group of people that you'd like to leave your FC to be with in theirs but you have to wait 3 days to do it. :X
It's also really not hard to farm credits in a day if you really wanted to (spamming crafting/expert delivery/alt character progress, etc.).
These changes just seem like a way to screw over the Average Joe rather than fixing submarines. The only thing that will actually fix it is removing it from FCs and making it something everyone can access via Grand Companies.