Subscribe to ICS feeds
I use a number of other services that provide ICS feeds for calendar events (Remember the Milk, Basecamp, etc.). It would be really handy to be able to add those URLs as calendars to my calendar so that I can view all upcoming events and tasks in one place.
Seconded. One of the reasons I can't yet leave GCal is that I can subscribe to ics calendars such as for sports teams, etc. Specifically I would love to be able to subscribe to my Todoist ics so that my "to do" items were automatically on the calendar. Or better yet, contact the Todoist people and find out how to all users to tag their To-do list items with "Protoncal" like we can with Gcal and have two way integration so if I change the item on my Google calendar, it auto updates the items in Todoist.
That would be very helpful as I would be able to use ProtonCalendar as my primary app then. Currently I'm disabling encryption with full external link sharing.