Right. Just open up the casting to include women, and if a woman has the best audition, then cast her. Don't cast a woman because of outside pressure (ie, those articles on blogs that come out every so often titled "When will The Doctor Be a Woman?" etc), as a ploy to increase the flagging ratings, or to attract publicity.As you said, as long as the actress is cast because she would be good in the role, and not for the sake of being a woman, then the casting is not a gimmick.
It reminds me of what they said once about Matt Smith's casting. He was the 3rd or 4th person they saw, and they immediately loved him, but they pushed on and saw dozens of others anyway because they didn't want to cast without sampling others. But his audition still stood out as the best at the end of it.
That's the right way to go about it.