Basically the Home Assistant app on Android/iOS just needs to be able to sync the calendars down into the internal storage on the phone. Similar to how the Outlook app does it.
With Pebble watches being revived and making a comeback I would like to get my calendar from Home Assistant to work with the watch. My wife and me strictly use the local calendar in HA for everything so being able to get notifications about these events on my watch would be awesome.
I know an alternative is to sync it to a calendar that is supported on the phone but I do not want to do that. The purpose of using the HA calendar is to avoid third parties having access to any of my calendar events.