While it's clear that there's still plenty under wraps, we are seeing more details about Windows Mobile showing up today.
So, what's the gist of what's coming down through Microsoft's pipe? Everyone knows that Windows Mobile 6.1 is coming through the tubes, and that it's a relatively small update. It does some stuff that will be awesome (threaded messaging, for example), but beyond that and a few minor key tweaks, nothing fundamentally significant will change for the people using it.
For the next version after that, Microsoft is going to pare down their desktop version of Internet Explorer and stick it into Windows Mobile. Core apps like Office, Outlook Mobile, Windows Media, photos, etc. will all be re-vamped (re-imagineered?) so as to be easier to use. It sounds like the tweaks will be subtle enough that it won't freak out long-term users but still deliver some good, solid UI improvement payoff.
The next version of Windows Mobile after that last version of Windows Mobile is going to get the crazy redesigns, fully integrated search love, and should be able to present information to you based on your context. For example, while you're on the phone with someone the screen shows you their card in your address book, or a driving map to where they are, or the meetings you have with them in the next 2 weeks, or the next 20 emails you're going to send to this person. Microsoft will no longer optimize Windows Mobile for styli at this point, unless you think of your index finger as a stylus.
At this point, with 6.1 and then the next and then this version of Windows Mobile getting rumored, I don't know where to put the codeword "Photon." My guess is that it applies to all of them and none of them. Might be time to retire that particular codeword.
At the recent CTIA conference, Ballmer was asked about the Zune phone. As usual, he dodged the question, but said that they'd probably roll achievements from the Zune into Windows Mobile. As to which version of Windows Mobile will get those improvements, we've got no answer yet. Unofficially, it sounds like piecewise into both of the next big versions. At any rate, we know it's coming someday.