I don't particularly buy this argument that a low/no APD at EDI will have a serious effect on NCL long distance. The paying punter is only interested in the total amount of money the fare (or whole trip if they are a bit more sophisticated) will cost. If just cost, and not the convenience of flying from the local airport is not a critical part of the selection process, NCL would have nearly no long distance pax. Whenever I'm off anywhere, and the cost is coming out of my pocket, I always look at fares ex MAN and LHR (as a minimum) as well as NCL, and most of the time, the cost ex LHR is way less than NCL (I mean even after taking into account the travel by car or train and potential hotel associated with LHR), such that sometimes it is definitely worth the aggro - the fare differentials can be way more than the value of the total APD.
Similarly with short haul, the premium you can pay for flying from NCL vs LS or MAN or EMA (and especially LTN,or STN or BRS) if you are prepared to travel a bit on the motorway would suggest that if this was a consideration, NCL would have no traffic at all. I just don't see how some cheaper net fares ex EDI will outweigh the pedestrian traipse over the single carriageway speed camera alleys of the A68 or A1, and then round the Edinburgh by-pass (remember that many people on here complain about the relative inaccesibility of NCL from south of the Tyne because of the western bypass!). Nor the cost of ECML train fares at peak periods (unless Salmand is going to subsidise those as well !).