Co-axial rotors are insanely complicated. The V-22 had to overcome many first time problems and is very complicated. Combine the two, and you'll have a bunch of weeping engineers and no product.
On a co-axial rotor:
- Both the rotors need to have their individual swash plates being able to generate collective and cyclic inputs. But one swashplate is above the other.
- if the rotor heads are fully articulated, there needs to be enough distance between the two to allow for differences in flapping dynamics. But a rotor high above the helicopter creates a bit of a construction problem.
- The rotors turn in opposite directions, requiring two different sets of gearing & drive train, all sharing the same axis centre line.
Aerodynamically, co-axial rotors can deliver a higher end thrust than a single rotor of the same diameter, at the expense of less efficiency: the same mass of air is accelerated to a higher velocity. The obviously less complicated solution of a greater diameter rotor, accelerating more air, runs into its limits when the blade tips approach supersonic speeds.
The Osprey tilts its rotors to be able to fly faster than a horizontal rotor helicopter, the limiting factor again being blade tip speed, but now in the propeller way. The Tu-95 does use contra-rotating propellers, to be able to fly faster than with single propellers with the same thrust.
So yes, aerodynamically two sets of co-axial rotors would have benefits for the Osprey. But it would be an impossible engineering challenge, the Osprey is pretty complex and had plenty challenges to solve as is. Have two sets of co-axial rotors and tilt them? No way.