I have always thought that a single ENY value for a plane does not make sense. Take the P51 for example, should the 4 gun package with no bombs or rockets have the same ENY as one fully loaded with everything? If changed, the P51 would not be able to carry 1000 lb bombs past a certain ENY value. The 500 lb bombs might be restricted at a higher value. It would be limited to no bombs at some ENY, but still available otherwise, etc. Rockets, drop tanks, fuel level, gun package could all be factored in somehow.
This system could allow even a small ENY to make an impact without preventing access to the popular planes, at least in some configuration. Not sure how practical this would be to implement, but would allow for more options than the current system.