Wow! Sudden burst of responses!
aaronp - the idea would be that this would supplement the zone controller rather than replace it - you could control the zones through the Media Center using an MCE style interface, but you'd probably want a controller somewhere in the house too.
pluckyhd - I thought about making it so you could remove the music library completely from Media Center, and have a ZP80 (for example) sitting next to your Media Center. The Sonos music library would show instead of the MCE Music Library, so you would see seamless multi-zone audio (from an end-user perspective), just using ZonePlayers rather than using the MCE output for music.
Chris - the technology works on extenders too, so yes both console and extenders would be able to access the MCE zone controller. The other thing it would enable is wall panel control (assuming a fairly powerful embedded Vista system in the panel :-)
MusceLondon - the key difference between Sonos and extenders is the syncing of music for party mode, but also the absence of a UI requirement for control. During the few days of summer we had this year, we had an outdoor party where I just picked up the zoneplayer from our bedroom, and took it outside, along with a pair of bookshelf speakers. You just can't do that kind of thing with an extender!
MrTybalt - the MCML is the easy part... I've had a look at the Sonos controller from purple.org but ultimately I'm going to need to write my own interface (it's not hugely difficult, its just that the majority of stuff you need to do isn't documented), as ultimately it would be nice to be able to sell this type of thing to custom installers/integrators. If you are still considering commissioning a project though, let me know!
Cheers,
Andrew