When women’s sports become totally transgendered, there goes the athletic scholarships, not to mention few spots on the team. Are they still calling it Women’s basketball and volleyball?
The first limiting factor now is that there are vanishingly few transgendered people, and even fewer who are highly competitive athletes. BUT: if female professional athletes ever started making big bucks, this would change overnight. Plenty of second tier men, especially the homosexual men, who can't make a pro roster in men's sports would be happy to announce as trans, at least for the duration of an athletic career, if the pay was right. Given that surgery is no longer required -- and even the requirement for hormonal dosing is under attack -- there would be no shortage of men who would chase the money.
The second limiting factor is that women's sports don't have a great public following. The public perception will shift dramatically when trans women start competing in, and dominating, sports that a lot of people actually care about. I would expect this to happen first in golf or tennis, where female champions do earn some change. Will the public stand for a bearded "lady" winning women's Grand Slam tennis events or LPGA tournaments? I don't think so.
The most popular women's team sport is soccer, where the USWNT is perennially among the world's best. It has a healthy fan base, and soccer will probably be the first women's professional team sport to become really successful financially. (The WNBA is a pure subsidy league.) It's bad enough to have sexually confused boys winning a scattering of high school state titles in competitions that no one watches aside from parents and boyfriends. But I do not think fans will accept players like Rose Lavelle, Alex Morgan, Christen Press or Mallory Pugh being cut to make room for female impersonators.