As it is, we only have a choice of one portrait per race/gender combination. I would very much like to see more variety on this front. In addition to extra options similar to what is already available, it would be really nice if they could pull your portrait from your lodestone like many of our signature banners already do.
However, I'd stop short of allows us to use any custom image we want. I've always found that mildly distracting on other forums.