... I am actually really into this idea, huh. But okay, so, the current checkboxes are "member", "can post", "administrator". So do we want to add an extra checkbox for "additional permissions", or do we just want to replace "administrator" with "additional permissions"?

And then the Additional Permissions management page could do the thing where you do uh

username | administrator | permission 1 | permission 2 | permission 3 | ...

... where "administrator" is a master-ticky that checks all other permissions automagically, or you can grant a subset?