I recall having a conversation years ago with an old friend. He had ridden in the 50's - until he could afford a real car - and had Enfield 350 at one time. He was looking at my pre-powervalve RD350LC and asked about fuel consumption - guessing that with the years of progress it should be doing 70 or 80+ mpg as his old Enfield did 50+ mpg. He was astounded whan I told him it did mid 30s - muttering about how his old Enfield was much better and even his mini was as good as that. When I suggested that we look for a bike of his era that could perform as the RD, or a (then) modern car that could we could then compare the MPG and see. As it was we could not find either - lol - but I know cars with the RD350LC performance of the time were doing low 20's even mid teens. My 750 ARE Triton could never match the RD for whizz - though it could just about top it for top speed.
So where am I going - bikes are currently seen as toys and as such most people want whizzzzzzzz in their toy, some want mud plugging ability a few want long distances in comfort. Not enough want cheap miles. A modern sports bike, when compared to a car of similar performance will come out quite well - even on the number of seats and luggage capacity. Unfortunatly many people still see bikes as a poor mans alternative to a car, and thus compare them to poor mens cars.
However I would like to see a reasonable bike with good MPG - I think it would be a good thing - but it would not sell in the UK because of the perceptions people hold of bikes - we need a lot more "Long Way" wherevers to change this and a nuclear strike on the MCN offices before the mainstream of biking will shift too.
R