Very interesting concept. We were actually heading this way with the first version of Raft (http://www.joinraft.com) but realized the huge amount of work it would take to be the content provider tasked with maintaining enough relevant and localized content. This made us narrow it down and focus on making it possible to easily follow calendars that most people are interested in, the ones belonging to our loved ones and friends.
A thing that puzzles me is why you are suggesting that Apple should pioneer this? To me this feels like a third party app and building for Apple Watch and reading/writing to the native iOS calendar is open for all.
There are a couple of services like http://www.upto.com that are trying to own the space of subscribing to calendars of your favorite TV shows, brands and sport teams but granted that they could do it in a more engaging way.
Nice to see you writing again. Enjoying it ☺