APD
I follow your argument that what is fair for Scotland is fair for Wales and Northern Ireland. So is it fair for England to remain under the yoke of the Westminster parliament for such matters where Scottish, Welsh and Northern Irish MPS would have a say on English APD, where the rates would remain draconian, as well as on many other purely English issues?
That's the rub and a tricky conundrum for the new government to ponder.
If the Wales Assembly Government was given APD powers and reduced the rate to zero and it did lead to long haul (and possibly other services) starting at CWL when they might (on a level playing field) have gone to BRS, and even some current services moving across the estuary, the additional jobs created in Wales would obviously be a boon to the Principality. The jobs lost in the West of England would attract the opposite reaction there.
Most politicians and governments aren't interested in fairness, only expediency. Apart from three Labour-held constituencies in the middle of Bristol the entire BRS core catchment and well beyond is a sea of blue in political terms. The new government will be wary of upsetting their new power base in South West England that was a Lib Dem stronghold until this week.
So APD devolution to the Wales Assembly Government might not be the tick box that some seem to believe.