They currently have a vCard-like syntax.
Interconversion with an XML syntax would not be hard,
but nor does it seem particularly critical.
They seem to be mostly working now on CAP, the protocol;
the model/syntax (iCalendar) seems stable.
I think they are still debating whether CAP will
be an HTTP extension, or use existing HTTP POST/PUT, or be a
different protocol (like SMTP/NNTP/etc.).
-mda