My own liking for a docking station (which should ideally be portable enough to use on trains etc) would be:

• a few USB ports (2-4 would be sufficient)
• built-in USB ethernet (and possibly serial)
• power connector which charges the docking station's batteries as well as the 770's
• pass-through for headphones
• VGA out would be fantastic if possible (are there USB -> VGA interfaces?)
• Built-in stand for propping the whole thing up
• Slotted in 770 with some kind of restraint to keep it in once docked.

A larger unit which allowed the inclusion of a 2.5" laptop HD connected over USB could also be very interesting.