It strikes me that with its wingspan coupled with the rotating blades, the V-280 is going to need a very substantial clearing / vessel / landing mat / parking apron from which to operate compared to the current UH-60, or even Sikorsky-Boeing's SB>1. Have tried Googling the V-280's dimensions, but no joy coming up with any measurements (maybe just looking in the wrong place).
It might also have been mentioned already, but surely any forward firing weapons would be inhibited by the V-280's two huge rotor discs (FVL-Medium is after all supposed to replace the Black Hawk and Apache)? The only imagery I have seen of the V-22 firing rockets shows the engines in the 45% angle.
All in all, I think the SB>1 is the far more practical solution (assuming Sikorsky-Boeing can overcome their current technical difficulties).