I already made one! I also made some matching panties to go with it. The garments are made of linen and are embellished with lace, as close to period needle lace as I had on hand.
I have more pictures on my website: http://www.faerie-queen.com/15th-century-bra-and-panties/
And here is an article on the bra: http://www.historyextra.com/lingerie