By the way, I see you edited this from the first time I read it - I should point out that FastMail provides a full CardDAV/CalDAV service and uses VCARD under t

By the way, I see you edited this from the first time I read it - I should point out that FastMail provides a full CardDAV/CalDAV service and uses VCARD under the hood as well (it's the Cyrus IMAPd server) What we do need to make sure works is extensibility and custom properties, because as you have correctly pointed out - we can't tell what's necessary for the future. I really want to make the extensibility not be at the expense of the simple things working well and reliably though. I see a fetish in standards bodies for edge cases and complexity. We want "making the simple things easy and the hard things possible" not "making the hard things possible and the simple things hard". The whole user principal dance in *DAV at the end of which there is STILL no standard way to share calendars/addressbooks - all the DAV sharing stuff is basically unused or semi used, and the whole use of collections is pretty much ignoring the capabilities of DAV.... that's crazy. It's layers upon layers and you get crap like Evolution depending on seeing that the PUT action is allowed on the collection (which it's not in Cyrus, because you can only put resources with in the collection) and marking the calendar read-only. Really? Even bootstrapping is a fraught nightmare. That's what we want to avoid with JMAP - a million choices and all of them horrible, with no clear guidance.