The nursery for ballet choreographers needs to start at the high-school level, and needs to take root in the major ballet schools. An apprenticeship with a major choreographer (i.e., Peck, Wheeldon, etc.) would be an amazing start for anyone, female or male. I know SAB female students are being heavily encouraged to go outside and explore other choreographers besides Balanchine. They are also given a lot of rehearsal and performance time to show their pieces to the Board, family and friends of the school.
Perhaps major companies should spotlight these young choreographers in between their popular ballet pieces during the season. What a treat it would be to see young talent showcase their pieces to a paying audience.