After digging a little bit about it found the icalendar python pacakge which is in active development and supports py27 and py33+. This package can be used to generate a ics file for any data in the tryton database. They have examples on their documentation.
I found this interesting to expose calendar using a custom route (and manage authentication if required) to third party users (or to mobile devices). I don’t know if we should have some example module in base (like we do with authentication_sms).
And I agree to the proposal about replacing party_vcardav