Well, the two transmissions are very similar, and still use the same engine. I would assume the 6R80 would fit. But since I have not done it, I do not know. It may come down to how deep your pockets are.

The 6-speed 6R75 is not a bad transmission, but it does seem to have its own little gremlins. I have not had any issues with mine, so far. It has a Mechatronic unit inside the transmission itself. It will learn your driving style and other information over time. Information it collects is saved in the Mechatronic unit in non-volatile memory.
So if the battery is disconnected, the shift data is not completely lost. The 6R75 will simply revert to its last saved data entry.

The tyranny itself is fairly robust, virtually the same as the 4-speed 4R75 it replaced.
On the shifter there is a small circular button with O/D on it. By pushing that button, the 5th and 6th overdrive gears are disabled. The 6R75 is denied access to them.

The 6-speed 6R80 is the new and current transmission used in the Expedition. It is also used in the new 2009-onward Ford F-150 and its many versions including the SVT Raptor.

It has slightly more robust internals and includes tow/haul mode instead of overdrive lock-out. Tow/haul mode alters the transmissions shift logic for uphill/downhill, towing, hauling, etc. Primarily the transmission will hold gears longer before up shifting. This also helps to keep it from hunting.