Yep Voldara brings up an excellent point. While useful, a system like this would be open for abuse by malicious managers, and it's hard to prevent such occurrences while also providing such freedom of expression.
It's a tough thing to balance.

But still, while there isn't a function in the game that helps out with inactive F.A. Captains, there is the option of writing to our support team about this.

BUT please remember the following rule - A support agent will relinquish the Captain title from the current captain of your FA groups only in the case that said captain has been inactive for the past 30 days.

If you go to support with such a request I would advise that you chat about who will be the new Captain of the group, in the FA chat. Vote for it among yourselves.