I think the biggest thing in this election was rise of English nationalism through UKIP and to a lesser extent the Tories (English votes on English matters).
I suspect that APD won't be devolved, especially when you've got MPs like Liam Fox in the SW England region who is quite happy to do a bit of rabble rousing. He may or may not like the airport but he'll respond to people complaining about Wales getting beneficial treatment (there's already grumblings about this in the border areas).
If Wales does get APD then money might be magiced from somewhere to pay for something like making the A38 a dual carriageway, which when coupled with the southern distributor will make BRS a lot easier to get to.
There might also be an element of becareful what you wish for, Wales will get APD powers, but any tax cuts will need to be fully paid for by Wales (i.e. not made-up via the Barnett formula) either through spending cuts or raising other taxes. The real sting in the tail would be the shortfall being calculated based on the hypothetical APD that would have been raised - so as the airport gets more popular more tax revenue is lost and has to be made-up for elsewhere.