A little early to be suggesting this, but after the mod ports I'd love to see Elenai Dodge 2 support. They add a feather bar for their dodge system that I think could be utilised by this mod's flight system. I basically propose a config option that makes flight drain feathers rather than hunger; this could make flying with full armor much harder compared to flying with no armor or light armor.

And also, heavy armour like Iron should also make the wings slower.

Good idea, but it could easily be worked around if you just take off your armour then put it back on when your done flying. Also, certain wings should drain the feather bar slower then others, like the Butterfly wings should drain it very slowly.

Indeed, but the feather bar drain speed should be configurable just like the hunger drain speed currently is.