Even if you don't consider diving to be a "mainstream" sport, there are all the out ladies at the top level in football, tennis, cricket and hockey, plus Gareth Thomas who came out while playing top flight rugbi, and Nigel Owens who might be the best ref in world rugbi.
I've pleased to see that all the BTL stuff I've seen on any of the news items about Philippa has been positive however - gives one hope in society.