Hi, I'm an engineer working on X2. I find the discussions going on here interesting. Though I can't really comment on what hasn't been publicly disclosed, I will say this, the people working on it are some of the best in our company, if not the industry.
The ABC struck me as a good idea and I wanted the company to revive it as well, and soon after the X2 program was started in 2005. Seeing it from the ground up has been a once in a lifetime experience, and being there for first flight was one of my most cherished memories.
Dave, I've gone through your site, and appreciate your collection of information there. However, I feel you've been knocking our small team unfairly. Not quite sure what limitations you are referring to but let's go through them shall we?
1) Vibration - ABC vibration was wicked at high speed. I mean the instrument panel was a blur! We are using AVC (in a novel way for Sikorsky), as has been stated in the press releases. Besides that we have a 4 bladed rotor, which helps. Test pilot comment is that its like sitting on a couch watching TV.
2) Loads - ABC vibratory loads were quite bad, due to hingeless rigid rotor at high speed. It also had high maneuvering loads. Obviously we have better materials to handle the high loads now as well as fly-by-wire.
3) Performance - L/D ratio was just as poor as every helicopter, 3-4. Though we don't have the 250 knot data yet, I expect we will double that. I know you've gone through Mr. Bagai's blade patent. I work with him and can tell you that figuring out the final solution was not easy. The shaft fairing, which can be seen in the popular sci article is another important invention for reducing drag.
4) Workload - the ABC required 2 pilots to fly. X2 has 1.
5) Acoustics - The ABC J-60's were loud. A prop can be clutched.
So...I'm sorry its not a Synchro (honestly, I doubt there would be much difference with a synchro ABC vs. coax...we can discuss if you wish), or that it doesn't go 400 knots like the Russians claim their magic VTOL does. Ideas are a dime a dozen in this industry. What matters is putting your thought into action, design, build, test, and fly!