Larian already have experience with creating very good flying with WASD. In Divinity 2 they were applying a bit different control scheme when you would turn into the dragon. It may work here as well. Just if you're flying, you have different controls. And it may even be hybrid of those 2 control schemes. Like this:
1. Click on the ground still works as "go there", without change of the flight height.
2. Each time the player presses X-botton for example, the character goes a bit lower.
3. Each time the player presses Z-botton for example, the character goes a bit higher.
4. Click+X means "land there".
5. Click+Z means "hop up as high as possible there".
