Lawren, thank you for this post because it compelled me to chime in elsewhere when previously I had dismissed those "man-bra" threads.
Like many girls here, I have no use for this and as far as a marketing idea, it'll likely go down in flames. Men have no want or need for a man-bra. If they do, they're likely tg of some sort. And as evidenced by the replies, those of us in tg land overwhelming have no want for a man-bra either. The concept will likely persist only as a joke. Women might buy something like this as a bedroom gag for their guys but otherwise, I fail to see a sustainable market.