I have no problem with a female becoming the wielder of Mjolnir and thus goddess of thunder. The problem is that, despite their statement, they are essentially producing a female clone of an existing superhero.
For the moment.
Mayhaps you are not aware of this has turned out in the past? I suspect the female Thor storyline is merely the origin story for a new female superhero. Thor falls from grace, she picks up the mantle. Thor eventually cleans up, and she continues on as a hero of some form or other afterwards. Beta Ray Bill and Thunderstrike were both granted their own weapons after beign worthy of Mjollnir, so I expect this to be the pattern here as well. She'll be the thunder goddess for a while, then she'll be her own hero.
This does seem to be a somewhat odd move - to a certain extent the comics and the movies now feed back into one another, which means that Marvel should really be seeking to keep the character identities in sync - Captain America should be Steve Rodgers (and should look pretty much like Chris Evans), it needs to be Tony Stark in the Iron Man suit, and so on.
I don't think it matters that much. Comic fans understand that the two universes are different. Non-fans won't care.
We do know that Chris Evans is under contract for 'only' three more movies (Cap 3 and Avengers 2 and 3). And, unlike in the comic universe, he's not immortal and unaging.
Chris Hemsworth is on record as saying that, keeping up the Thor physique through Avengers 3 is *not* going to be easy. He'll be in his mid-30s when Avengers 3 comes out, and keeping up that build into his 40s? Unlikely.
So, if Marvel want to continue their movie universe indefinitely and avoid reboots, they'll need some sort of succession plan - either new actors take over as Steve Rodgers, Tony Stark, et al or (perhaps better) they retire the original superhero and bring in a successor.
So perhaps this is them starting down that road - use the comics as a test-bed for a new Cap (and Thor), and if it gains traction then they can make the same change in the movie universe. And if it doesn't work out, they can do something else instead.
I don't think so. The current plan has Avengers 3 out in 2017. Tests today won't mean much by, say, 2020 when they'd be really trying to recast. At least, not any more than the tests they've already doe in the past - Cap, Thor, and Iron Man have *all* been other people in the comics in the past.
I think this is where the "Phases" of the Marvel strategy come in. The first Phases amount to "Take some of our most iconic heroes, make really good movies". Now, they start to play off the accumulated good opinion - with things like Guardians of the Galaxy and Ant Man. Broaden the stable, use more Marvel IP, but try to keep the movies good. Soon, the word becomes "If it is a Marvel movie, see it!" Marvel has so much IP to play with, they can then take their time with recasting / revisiting the Avengers.
I think the things happening in the current comics continuity are far more simple - response to public desire to see superhero universes show more diversity. After a run as Thor, the new female hero may have some traction. After a run as Cap, Falcon will get a boost when he returns to his more normal duties. By that time, the Netflix shows will hopefully be running (with Jessica Jones and Luke Cage), Agent Carter, and so on.
