I'd guess he's not bashing contrails, just remarking that we currently lack the conditions for them. However, there's been a surge (or at least it seems there have been) of "realism" ideas that mostly involve ways to avoid fights, prevent fights, stop fights, or cause planes to spontaneously blow up. It seems the majority of these requests are geared toward making AH look like il2, fly like a hardcore simulation, and have all the air to air action of watching paint dry. Adding contrails would be, IMO, the only reasonable request in the list. I don't know the alt/temperature/conditions required, but arbitrarily giving any plane above the cloud layer a contrail would add some eyecandy and a means of picking out distant cons without being too gamey. Would probably take some tweaking, but I'd be in favor of trying it.