The bad news has finally been confirmed by Microsoft [MSFT] saying that the HTC HD2 will NOT be able to get a Windows Phone 7 Series upgrade. This was kind of revealed last week, but not through an official channel.
For a few months there were a few hints around from various HTC Twitter streams as well as some information from Adobe forums indicating that the HD2 might be getting the update, but just last week some information was put together showing that the HTC HD2 doesn't meet specific hardware requirements that Windows Phone 7 Series demands.
In particular Windows Phone 7 Series devices much have three physical buttons on the front of the device, the HD2 has five buttons. Also other restrictions within the hardware (nothing confirmed technical wise) is believed to be another factor. This could include the graphical capabilities of the device not being up to par.
Engadget pointed out that every MS employee seemed to have a HD2 at the meet up today. If you do happen to have purchased a HD2 then I guess it's bad luck if you were hoping to get the WP7S upgrade. However, it's still a fantastic phone even on Windows Mobile 6.5, so should give you some years of life out of it.