Although gyroscopes are expected to the big hardware change in "Mango" (along with some new CPUs), front facing cameras are sort of up in the air--nothing official from Microsoft on it, yet it doesn't seem forbidden either. Going further, now that Microsoft owns Skype, video calling all but seems a certainty at some point in the OSs continued development. (There were also some rumors awhile back that front-facing cameras were coming from @MS_Nerd)
Looking at the Windows Phone 7.1 SDK, we can still see the SelfPortraitCamera enumeration value listed. We say "still listed" because it is technically not new--it's been there since the 7.0 SDK but obviously was not put to use. Seeing though that MS has yet to remove it, there's a good chance that (a) WP7 has always been meant to have a front-facing camera and (b) it's still on the table.
Whether or not the APIs go deeper than that and the software can fully support it is another matter. The early Samsung Taylor developer devices did have a front facing camera, but ultimately the hardware was either not active or the APIs were yet to be written (or both). However, those 1st generation phones also lacked 4G--something that is added in "Mango" and usually desired in the U.S. for phones with front-facing cameras. Having said all that, we're betting on later "Mango" devices to have ff-cameras, just because we dont' want to get our hopes up.
Update: We've received confirmation from a trusted source (i.e. you've heard of him) that the new Mango hardware specs do list front-facing cameras, meaning we can expect some video goodness from some OEMs in the fall. This is looking to be confirmed, at least from our standpoint.
via: Leon Zandman (Twitter)