Isn't CardDAV the only missing piece? MfE may be the only possible solution for some people, but harmattan does IMAP IDLE, we have CalDAV as the only way to sync multiple calendars already - the only missing functionality is contacts syncing.

And if you would've used that sync for backup only, a Nokia account already does that.

So really, barring bugs in the client or server, CardDAV is the only thing we're missing out on.