I think I remember Nepenthe posting something about Sea of Blood and how it broke trying to implement items sinking. This idea is similar: If you are in the air and your fly runs out, you fall. For example, in the air above Galadon, instead of being stuck, you fall when your fly runs out and you take massive damage or die in the streets of galadon. Makes perfect roleplay sense, and indeed it doesn't make sense with the current way it is. I can understand if it is too hard to implement.

P.S. I got a laugh when I 'tap self'ed myself underwater