In this society, there is no gender inequality. Ian's own "A Few Notes on the Culture" essay http://www.vavatch.co.uk/books/banks/cultnote.htm states it best:
A society in which it is so easy to change sex will rapidly find out if it is treating one gender better than the other; within the population, over time, there will gradually be greater and greater numbers of the sex it is more rewarding to be, and so pressure for change - within society rather than the individuals - will presumably therefore build up until some form of sexual equality and hence numerical parity is established.
Until our science invents this, this is a great thought experiment to conduct.