The reason you can't currently do long hair or longer beards is that they would have to extend off the current 3D model of the players head (i.e. image that the current 3D player head model is a styrofoam wig manikin and all you have is a sharpie. You can draw a mustache or short beard or short hair on the manikin but you can't draw off into thin air).
I think it could be done as I detail here:
http://www.ootpdevelopments.com/boar...ow-bobble.html but OOTP would have to add a few transparent surfaces to the model for us to draw on.