Bell has been going back and forth between tilting just the rotor or the entire nacelle for decades. Here are some images of the Bell XV-3 tilt rotor from the 1950s and 60s:
In the XV-3 case, the single radial piston engine was inside the fuselage just aft of the wing-fuselage junction with a transmission and drive shafts carrying power out to the wingtip counter rotating blade assemblies. With only one engine, the need for cross shafting between the rotors was eliminated since loss of engine torque would affect both rotors equally and not produce asymmetric rotor power.
That’s the problem with twin engine tilt rotor designs; it requires cross shafting from one nacelle to the other so that the rotor with the engine out can continue to receive power from the other engine. Makes for a complicated wing structure. (It’s even more complicated when the blades must fold and the entire wing must rotate to align with the fuselage for shipboard stowage purposes.)
If the VX-280 power plant/tilt rotor design is scalable to the MV-22, I suspect the Marine Corps and other users would only be too glad to get out of the tilting nacelle business. In the meantime, I hope a solution to the MV-22 deck/runway heating problem can be found. Perhaps a variation on the jet thrust reverser to redirect the heat (most of it anyway) upward where the turning rotors could disperse it?
Have they never considered a ducted fan design instead of rotors? At altitude, at least, troops could bail out in an emergency, without getting chopped to bits by the rotors.
Already, any rotor-failure looks like it’s going to instantly cut the fuselage in half.