Though I disagree with the move, it 's likely to have almost no impact.
For a long time, the CIF rule was if a school only offered a sport for one gender, then a person of the other gender who wanted to play was allowed to. (The thinking was football and wrestling ...)
But the sport that would have felt the impact was volleyball, as many schools had only girls' volleyball teams at the time. There was a lot of loose talk about boys taking over the sport by playing on the girls' team, but it never happened -- and there are a lot more athletic boys in a given high school than girls who used to be boys.
About 3% of teens identify as transgender, and it appears more want to go girl to boy than the other way -- so say 2% of a high school population is transgender girl to boy (g-b). In a 2,000 student school (which is large here), there would be four girl to boy transgender students. Most transgender kids are not achievers, but let's say three of those four g-b transformations wants to play a girls' sport. Let's say two of them are good enough to shift the balance in their sports.
So one g-b plays volleyball and is all-league, and another plays soccer and is all-league. Now based on what we've seen before, it's likely neither will participate, but one might -- which will not, I don't think, really change things.
That said, it is an issue, and hopefully down the road what they'll do is say that a g-b can only play an interscholastic sport by appealing and getting a waiver. For example, I don't think a 5-4, 120-pound g-b will make much difference on the basketball team, so why not? But that 6-3 kid with big shoulders on volleyball? Not allowed.
The whole transgender issue is an odd one, and hardly worth the energy we bring to it ... we've a lot more important things to worry about.