User story: I’m part of an emerging group with a few people in it, and one or two involved in the project that haven’t joined the Karrot group yet. I wanted to create an activity related to the group, so it goes to my personal calendar and invite the person outside, who is regularly using calendar events to our appointments.
I noticed quite many people are used to creating an event in their personal calendar and sending them out to possible attendees, I believe using the iCalendar format. Why not do the same with Karrot, for public activities? 
Complexity: not sure, depends on how we design it?
Outcomes (or what needs to be done to move forward): check if this idea would be useful for other groups