Could you add brett to mead to make a sour mead. Or would that not be good.
To make it sour, you'd have to add a Pediococcus and/or Lactobacillus culture.
I brewed a sour mead recently that is very drinkable; I think it will age well. If you search sour mead on the forum, you should get a few good hits.
Take a look at this thread.