Its really a simple idea and should be easy enough to implement, since the similiar functionality already exists with overviews, but let me explain what exactly my idea is.
I would like to see the addition of being able to create custom calanders and being able to share them with other people who then can subscribe to that callender and of course unsubscribe again, once they do not want to follow the events of the callander anymore.
This would be a great tool for any group that is doing public events. You run public NPSI fleets? Great, now you can let ppl subscirbe to your calander and they will all know and be notified in time when the next event ist going to happen.
Your name is Mike Azariah and want people to know when and where the magic school bus is going to be? Let them subscribe to your calander!
You want to run any form of regular public event? Make your own calander and share it, so you dont need to rely on people seing your next announcement in the forums in local or wherever you are announcing your events.
This way people will not miss your events again.
edit:
It could also be setup in a way, that you can give rights to other people to enter events into it if you act as a group.