It’s still pretty rare, but not as rare as you might think – and it’s an upward trend:

…The idea that men can receive spousal support from their wives may feel like a freakish concept, but as women have become higher earners, it’s increasingly common.
And as men set their sights on women’s earnings, women have become more protective of those dollars. In fact, according to the American Academy of Matrimonial Lawyers, 44% of attorneys included in a recent survey said they’ve seen an increase in women asking for prenuptial agreements over the last five years, where in previous decades, prenuptial agreements were almost always sought by men.
A lot of women are indignant now that the shoe is increasingly on the other foot, says Carol Ann Wilson, a certified financial divorce practitioner in Boulder, Colo. “There’s this sense of, ‘What’s yours is ours, but what’s mine is mine,'” Wilson says. “My first response to that is, ‘All these years we have been looking for equality; well, this is what it looks like.’ I think women get angrier about having to pay than men do.”