Well, since the 55XX series was passed-over for the Windows Mobile 2003 Second Edition update (when the 55XX was just a year old), then it follows that the 63XX will probably also be skipped.
The HP/MS marketing types have shown (as of late) that they think that if they can squeeze another hardware purchase out of the consumer by limiting the distribution of a New OS to newer units only, why would HP want to bother spending the time and money tailoring the new OS so existing iPAQ users could install it as an upgrade?