What was the exact wording then?
"While we were shooting 'Ragnarok,' I was reading one storyline by Jason Aaron, 'The Mighty Thor,' and for those of you who know that storyline, it's incredible. It's full of emotion and love
and thunder. And it introduces, for the first time, Female Thor. So ... for us, there's only one person who could play that role. Only one. And she's here. I'm going to introduce her to you now. Please welcome to the stage: Natalie Portman."
So, yeah, nothing about the plan for this storyline introducing "the first female Thor" to the films. At least not as you worded it.
Could that end up happening? Sure. At the moment, though, we have no idea whether this is going to be a character actually called "Thor" or if this is just a character heavily based on the Jane Foster Thor. And we have even less inclination about how any of this -- whatever it happens to be -- will come to pass.
No one. That doesn't mean it isn't weird for another person to be running around calling themselves by his name instead of their own name.
It never struck me as weird in the comics. Maybe that's because I'm so used to the X-Men, where it's mucho common to have multiple alternate versions of the same person walking around with the same name, or maybe it's because Thor himself bestowed the title on Jane.
If she does get the title here as well, I'd bet top dollar that the Odinson himself once again gives it to her rather than it being something she christens herself.
The source material took place in a world where Dr. Donald Blake, Jane Foster's friend was a real person that became Thor. Eric Masterson and Beta-Ray Bill had been a thing by then. In that universe Ragnarok had happened many times already and there had many incarnations of Thor. MCU felt all that was convoluted and unneccesary.
Well, I have to agree with them where Blake is concerned, what with the decades of going from where he was a) a human doctor to b) where he was just a magical construct and identity Odin planted in Thor's mind to c) where he had been a real guy who went into suspended animation when Odin had him supplant the poor man's identity to d) where there had been a real Donald Blake, but the one who had been in suspended animation actually was just a magical construct because the real dude had been vaporized before he could quite get involved ...
...
It's quite a mess, and not even one worth ever addressing again to unfuddle.
Thor is this one particular Asgardian who comes to Earth himself and doesn't need a human alterego, even when he loses his worthiness, he's still just Thor. That's cool with me, but I don't think it's silly to say that it is now not very well positioned to abruptly do a adaptation of the female Jane Foster Thor storyline.
We'll see what they do with it. It really shouldn't even be that hard to find a fitting method for this. Hell, give me a little time to think on it and I'll come up with an adequately comic-book-y-but-still-better-than-the-worst-kind-of-examples-of-that-(e.g.-the-Donald-Blake-thing) idea as an explanation even for Jane literally becoming Thor on some level.
