I suggested a permutation of this a while ago but made the mistake of mixing it with another suggestion, so it got buried.
TL;DR:
I think that the "aircamping" timer should be removed, and that the President should be allowed to fly Rustlers and aircraft slower than Rustlers.
I think the "aircamping" thing should be removed because it is unnecessary and discourages Presidents from flying. If the person flying the President (or the President, if he is allowed to fly) can land in a reasonably small space, then they can very easily get more health and the timer is simply an annoyance. However, I rarely see people even getting to that point because the President often flips out about the timer and either demands to be brought back down to the ground or jumps, which doesn't tend to end well. The timer is eliminating a whole dimension from the game (literally- a good portion of the Z axis).
If you think that removing the "aircamping" thing and letting Presidents fly will make it impossible to kill the President, consider that this is analogous to Presidents riding NRGs- a good stunter can outdo most of the server. However, there are always ways to defeat them if their pursuers are so motivated- get a plane and ram them off their stunt spot, or snipe them, or shoot out their tires when they're running. I often get thwarted by people who predict what I'm going to do (not hard, since I'm an NRG whore) before I even get going.
Rustlers are the same way- there is a finite amount of space that you can fly in. Anybody with a bit of strategy can force even the best pilot into sniper or AK range, or force them into a dogfight. Even I have a lot of trouble dogfighting two or more people at once. It's also extremely rare for me to go through only one Rustler in 15 minutes- I almost always crash at least one plane. I often get the President to surf on the wing of my Rustler, and it's fairly rare that I can pull it off for more than about five minutes (not because he falls, but because I get shot down). I often get shot down by people on the ground with snipers without another Rustler even being involved. If I can't always handle it, then I highly doubt that this will end badly if any President can fly and has multiple Terrorists coming after him.