I spoke about this with a dev before, not sure if you guys took it into consideration however. So I thought I would mention it again.
I would like to suggest calendar sub categories, inherit the permissions of their parent. That is the way, most forum software works, I guess this one does not and appears by other reasons. Forums aside, I would like that on the calendar.
If I do not want a user to see the parent category, I do not want them to see the child, however I may not want everyone that can see the parent to see the child either. In my case we do not, and only allowing on / off for each group, is not a very good permission system.
So in the case of my gaming community, we play a lot of different games. In those games, we then have PvP players, PvE Players, Crafting Players, Logistics Players. Each of those needs to be a sub group, of the Game. So now my options are, show all the events, of which there is alot, even when they dont apply to the person. Or make 60 groups for something that should only need 19 (15 games, 4 Content Roles)