I'd be very suprised if 3rd party widgets weren't allowed. The OS is still OS X and Apple have encouraged a lot of 3rd party developers to add to the list of widgets available to the home market.

I say watch this space, it isn't even available yet. If you're like me, in Australia, you have to wait until 2008!! Hopefully by then Apple will have 3G (possibly 4G in Australia by then) and built in camera capable of video too.

3x DSP5200 L, R and C (all vertical), 4x Triad Silver in-wall surrounds and 6x Triad Silver in-ceiling ATMOS speakers, Triad Silver subwoofer, Denon AVR-X8500H, JVC DLA-7500 4K projector and Screen Research 120" AT 2.35:1 screen.
Apple TV 4K and Oppo UDP-203 Blu-ray player.