My opinion is divided, and will be chosen based on the show.

Put simply it is like this.

If they have cast a female lead because their vision for the next part of this story would work best around a female lead as opposed to a male lead like the last twelve doctors, then they have my respect for being willing to break tradition and potentially piss off a lot of hardcore fans. I look forward to what they do with it.

HOWEVER, if they have cast a female lead more for the sake of casting a female lead, then they don't have my respect. By all means, cast a female lead, if the role requires a female lead. Dont cast it for the sake of appealing to the left.