The "SuperFan" engine was supposed to employ a geared fan in order to further increase the bypass ratio and overall efficiency by letting the fan rotate slower than the low pressure compressor and turbine. At the time, the concept didn´t come through and Airbus had to scale down to the lower-thrust engines used on the A340-200 and -300s. Only the re-winged A340-500 and -600 were able to use the much larger (but still conventional) RR
Interestingly, though, Pratt & Whitney now seem to have solved the original problems with the geared fan concept and have proposed it for use with the 7E7. As far as I know, Boeing have rejected this proposal, but if P&W can really make it work in practice with an attractive efficiency gain and at acceptable maintenance cost, it could still be used for a new range of engines - maybe even as an alternate choice for the A340NG...
FLUG REVUE October 1998: Pratt & Whitney PW8000 in development
Pratt & Whitney - News - Press Releases
[Edited 2004-04-11 02:55:56]