The thing is though, most of the quests that require flight will not even show up until you have attuned to all the aether currents in that area, so an icon to show on a quest that it requires flight is something of a moot point. The expectation is, once you unlock flight in that area, the game will assume that you will figure out on your own if you need to fly in that area or not to complete the quest.
Also if this is your fifth playthrough then you would know that a 'non-flight playthrough' of Heavensward is quite simply impossible after a certain point -
in the final area of Azys Lla you will appear in mid flight on a certain flying mount automatically during a main story quest as there is simply no other way to get to the Flagship and the final dungeon/battle except on Midgardsormr's back.
Naturally you can avoid it pretty much up to this point, but that part is pretty much the 'point of no return' of being able to get away without flying in Heavensward.