As far as I am aware, the tram route does extend to the airport, it was the heavy rail scheme that was cancelled. But yes, it is true that a vast area around there is underlain by shale workings and there have been numerous cases of subsidence. Somewhere on the north side of the old A9 road, a field had numerous warning signs on it due to subsidence.
I see a "Shale Pit " and "Ingliston Pit" between the runway and the River Almond. That could explain why they, seemingly stupidly, built the new terminal on the south side, when it would have been easy to reach it by rail on the north side of the site near the old buildings (not necessarily the north side of the runway), and why, much to my annoyance some years ago, when I would have preferred to use it, the old A9 was removed without an adequate substitute, in view of the volume of traffic in the morning rush hour.
A Mineral Railway ran almost parallel to the runway. Gone well before my time, as was the NBR South Queensferry Branch running north through Kirkliston. Apparently trainspotting forums frequently argue whether it was single or double track, if they bothered to go out and look, or study the old maps, they would see that it was single.
On the rare occasions nowadays that I visit Edinburgh it is by rail, which is very convenient. Perhaps just as well, now I feel safer that way....
I don't know the largest size of aircraft which is allowed to use Edinburgh, but can visualise an A380 with its tail stuck vertically in the air when the nosegear breaks through the runway into a crown hole.... The A380 seems to be very prone to mishaps.