RR is still investing in open rotor technology.
Rolls-Royce details next-generation engine studies
Even GE thinks it's the best solution longer term (leap-x in front);
http://i191.photobucket.com/albums/z...g?t=1247751620
Very high speed at height isn't essential for MPA, superior fuel consumption and performance at lower levels are more important.
RR has made good progress on open rotors during the last 3-4 years and are doing further tests as we speak. As you can see on the earlier sketches the front and aft rotor have different diameters and numbers of blades, reducing noise and vibrations (blades don't all pass each other at the same moment, shockwaves from blade tips don't hit each other).
The Bear and late eighties Pratt and GE open rotors where complicated in this respect. The Russians made some progress already
Saying it's a big turboprop with contra rotating props like the Shackletons and some Spitfires makes people more confident then using words like exotic "propfan"..
A second rotor makes the resulting airstream straight backward, a single rotor produces a more rotating airstream. Open rotor have bypass ratios of above 1:30, turbofan of 1:12 max at this moment.