From what Ive seen the eny restrictions havent done much to make people switch sides to fly what they want. I still see the same faces, many of those who complain in here regularly on how they hate not being able to fly their rides of choice. But still they stay with their side and fight.
To me and apparantly many in here, the game is more about flying with friends you've flown with for a long time, and the odd loyalties online games have. A person that switches to the lowest numbered side every time he logs on may be having fun, but I personally doubt he is getting out of the game, those that fly as a team, together do.
That said, I do like the idea of limiting planes in some way. But rather than making it a global restriction, Id like to see it affect damaged bases. Such as, if a base loses the fuel and ammo, then the ENY is set at like 24 or so, for that base. That would have the effect of slowing done a bases offensive power. A couple outnumbered guys could still get in and destroy those targets, forcing the high numbered side to resort to low end attack planes, or go elsewhere. (edit)The low numbered teams wouldnt be affected by this only the high numbered team.
The other undamaged bases could still support all aircraft making those that want to fly a certain plane happier, although they may have to fly a little further to use it.