Yes, flying is really cool and it would definitely be a sight for sure, but just imagine how many exploits would become possible by this on accident. None of the zones were designed with this in mind and if there ever will be one, the old ones still need an update. The only easy way to fix it would be a maximum fly ceiling which would ruin the fun of it. Unfortunately I think this feature will never make it into the game unless it is used in a fast travel sort of way like in WoW.