just to add to what bagginsbill has said, the only thing P4 users will miss out on is the use of V4 and V3 textures on the new eyes.  he's saying he'll generate shaders to transform textures and apply them to a new UV map on the fly.  and it seems to me that if the  "sclera + iris + pupil" are one material zone, then talking about edges between the non-existent zones is completely moot.  the edges are whatever you texture them to be.  it's like worrying about the edge of a  mole on the torso.