I do like this idea so long as it isn't overcomplicated.

It is a valid point to say that a new model for every helmet would be required if you got NEW hairstyles available. Changing between current ones would work, even changing it's color as most models cover and adjust the hair based on where it lays. the color would be the same.

As for adding eye colors, scars, dimples etc, that sounds pretty nice actually. I can't see it interfering with much.

To be honest though, I wish my tail color matched my hair color...