I agree that it could be something good. I think it need a special subroutine, but part of the job is already done, I bet...
The problem is not for your fleet planes, it is for your future planes...
I mean that if you already have one plane you can know the range thanks to "configure menu", but if you want to choose a new one you have no idea.
i.e.: I am playing in JA and I would like to know if a can reach a range of about 6000 NM with about 100/120 PAX with DC10-30 or Lockheed L-1011-500 and it is not so easy...