Thanks to the miracle of Photoshop, here's a doctored trail map of the Mittersill tract:
The area in pink was part of Mittersill's property, and is now the beginner terrain at Cannon. If you take the Taft Gulch trail at Mittersill and make the early exit, you end up at the top of the "H" lift.
The red liftline on the Mittersill side shows where the old Hall double chair runs. The top station of said lift is at the upper perimeter of the private Mittersill property. What Cannon wants to do is expand the liftline up to the peak (where Baron's Trail starts), likely to allow an easier crossover between mountains.
Most of the area within the USFS land is not cut as trails, save for Baron's Trail (which is kept clear by the Franconia Ski Club to allow easier hike-to access from Cannon to the lower Mittersill trails). So Cannon would like the extra acreage to be able to have a few more trails and a bit more vertical drop.
I fall on the side of keeping Mittersill wild - an "in-bounds-out-of-bounds" experience, similar to what is found at much of Mad River Glen and Jay Peak. The Cannon-Mittersill setup is unique as it stands, and in a great snow year (like the present one), Mittersill is New England skiing at its finest.