Let's just say that, based on what I know (admittedly limited) there isn't anything here the Army hasn't studied in depth before and rejected. Somewhere around here I have a summary of previous rotary wing R&D that I wrote in the late '70s (never published). There were several ideas for higher speed compound rotorcraft studied in the '50s and '60s - fixed wings, tail propellers, auxiliary jet thrust, variable diameter rotor systems, slowed/stopped rotors, etc. Eventually the Army decided that the speed range for the pure helicopter was just fine for the tactics expected in the foreseeable future. I haven't heard of anything in the roles and missions world that says the tactical role of the helicopter is expected to change to require higher speeds.
Remember also that money is very limited for the foreseeable future. Comanche was cancelled to pay for the helicopters we need for the current fight. Two of the ships we're going to buy are off-the-shelf to save money (LUH and my new program, ARH). The only major new helicopter airframe development program even in planning is a new heavy-lifter. Given the emphasis on the current fight, and the lack of dollars, a major mod program to increase speed doesn't seem like a winner at the budget table. Higher speed for a helicopter is a cool idea, but I'd place the odds of anything like the ringtail being adopted for production somewhere on the very slim side.
Dan H.
On the bench:
Not much right now, just getting started again.