As a woman of Nordic ancestry, with (an unspecified amount of) Viking blood in her veins, I am wicked excited to see how Marvel develops the upcoming female Thor storyline.
It did take me a few minutes to get used to the idea. In mythology, Thor is male; in comics, Thor was and is male (even during the whole frog thing ); in the general consciousness collective, Thor is male. How will the character, the personality, transfer to a woman?
If they can a create a multi-verse and parallel timelines, resurrect dead characters, and generally call an audible when they want something to change, is it really so shocking that a previously male character could return as a female?
I applaud them for being brave and trying something new that many fans will dislike; I hope it brings new fans, female and male alike, into the comics fold.
Besides, some frogs can change their sex from female to male. Marvel can argue that Thor is simply a reversal of that natural process.