The main thought is how are they going to ensure the blade structure at 400ktas? This will require at least active servos at the tips, especially as blade passes over nose at a reduced Nr. Still a compromise as wing will impede hover performance, and rotor will impede cruise/dash performance.
It looks as though they are going for a compressed air nozzle at the tip? With a high tip speed these can work, since nozzle area can be small for a given mass flow rate. I gather the problem is generally intenal drag from the need to duct high velocity air streams.
Good luck to 'em though - they'll need it!