Seafire6b. I think you are spot on about the future of APD. I think the attempts to tweak it are bound to fail. The only long term solution is to recharacterise it as some kind of environmental/congestion charge and apply it only at airports with excess demand and high environmental costs (ie Heathrow).
This is never going to happen under the watch of Messrs. Cameron, Osborne - and most importantly Johnson - it would really p**s off their "mates in the city".