I considered that but tossed out the idea. Why restrict something like that to usergroups? The only point in it might be for paid subscriptions. Its a relativly easy addon to make since its only a single option for a single usergroup. Simply use an if condition"is_member_of and you'll be good
I dont see a reason to limit it in any way since it doesnt really give any control of the forum. Its like making subscriptions usergroup restricted.