Hi everyone.
Players heads can be goofy without any customisation :
(26362244). ^^
Still, i really think that you will hustle before you will find players with crazy heads with that supporter feature, even in some seasons. Figures that wolph gives are very close to reality, and moreover, you should add all players created when a new manager signs in, and the fact that if you sell your draftee, no customisation possibility (for all those who draft and sell). The % of players with customized heads will remain so weak that your fear seems a bit exagerated IMO.
I will also add that this face customisation stuff is hugely limited : it seems that there just a single skin colour that matches the beard feature, I have seen no beard colour choice, not a single moustache and not that much hair colour choices... Seriously, what kind of strange faces can we make with that little stuff in store ? :°)