The addition of the ability to change the texture of worn player heads, currently player heads in the inventory and in hand can be retextured but there doesn't seem to be a way to retexture the worn item.

Also having the same issue, I believe it has something to do with this example below:
EXAMPLE FOR RETEXTURING PLAYER SKULLS WITH CUSTOM MODELS/TEXTURES:
type=item
matchItems=player_head
model=optifine/cit/skull
texture=flower_pot
nbt.display.Name=iregex:(flower pot)