To those saying "this doesn't matter because it will really only be a few people anyway": What no one talks about is that it doesn't matter if there are only a few trans competitors who end up actually competing in women's events. It doesn't matter if there are none.
Why? Because this change means that women's sport exists at the sole discretion of men. They can take it away whenever they wish. Train all your life, while you wait for the other shoe to drop, knowing that some man could drop his T and outcompete everyone competing in the prime years of your life.
Now, women's events and records will continue only so long as men choose to allow them. Get too uppity, start talking out of turn about how women are paid less in tournament play or how many women's team uniforms are demeaningly sexual in a way men's are not (ahem, beach volleyball!), and maybe you just don't need to be the best in your sport after all -- especially if you don't recognize your "femininity" and being ogled as the gift that it is.
Even if not one trans competitor enters the Rio Olympics, will people spend as much training their daughters in athletic competitions, assuming they were world-level athletes, knowing that men could barge in at any minute and take the biggest purses and collect all the medals?
The first time we see a bald bodybuilder with a clearly intact "package" medal at an Olympic event, maybe people will figure out that it's a problem. What they won't care about is the way that men have positioned themselves as the arbiter of womanhood, deciding spontaneously that hormone levels (something you couldn't even check on before seventy years ago) are the defining aspect of femaleness, rather than perceived reproductive capacity and genital configuration.
It's rather telling, isn't it, that the moment we unraveled sex hormones and discovered they could generate certain secondary sex characteristics when used cross-sex, that one single element of male/female traits, the one it was possible for lifelong pharmaceutical therapy to change, became the sole arbiter we were allowed to admit to distinguish who was male and who was female. Surgeries have a long way to go, but sex hormones, we've pretty much got a handle on and companies can make a profit from charging for artificial ones -- what a coincidence that these are the exact things that now determine your very maleness or femaleness.