What I do know for sure is that it‘s feasible for a calendar server to service both JMAP for Calendars and CalDAV. All our work in that regard is open-source in the Cyrus server [1] and is used at Fastmail.
Apart from the exchange protocol one also needs to convert between iCalendar and the data structures used in JMAP. For this, I am currently working on an IETF RFC [2]. Anyone also interested in implementing conversion between iCalendar and JSCalendar, please contact me! We have a test suite for interoperation tests.
[1] https://github.com/cyrusimap/cyrus-imapd [2] https://datatracker.ietf.org/doc/draft-ietf-calext-jscalenda...
We deny ourselves so much progress by forcing smart individuals with a passion into conglomerates that are merely busy destroying competition. Small to medium sized organizations have the biggest potential for innovation, and look what two people even can do.
I'm not trying to pick on this particular project, I just found out non-EU projects can apply at all. I hope the majority of NLNet money goes to projects that actually are executed in Europe and build expertise there.