Marvel has recently implemented some "changes" in its Comics Universe that may or may not be justified. They create these wonderful characters, get us to fall in love with them - then, they make someone else that character. Sometimes, this is NBD (as in No Big Deal). Sometimes, it just doesn't make sense.
I don't have any issues with a Black Captain America... the shield can be passed to anyone who can properly utilize it and has the skill to serve in the position. The uniform is worn by CosPlay Partiers all over the world! The "purpose" of the character is far more important than the "person" of the character. Make him of Oriental descent for all I care. I just want him to be an American. No Jihadists, thank you.
Falcon (Sam Wilson) fits the bill as a "Captain America" - in the comics, anyway. I don't recall him being a "Super Soldier" like Steve Rogers or Bucky Barnes - or even, as has been hinted, Black Widow.
But, Sam does have a history of athleticism, agility and intelligence (plus, he has experience with jet packs and wings and dodging airborne hazards). But, it could be a problem if he can't defend himself or take down high-powered bad guys. Agility and athleticism only go so far.
Bucky Barnes? Yeah... he's a Super Soldier from, apparently, Hydra Labs™. The Shield has been passed, what? Seven times? It's kind of like that ring DC's Hal Jordon picked up on a beach, one fine day... It works? Use it! No misfit here. GL's everywhere! There is no issues with who is Captain America - only that there is a Captain America.
As for a "female Thor". That's just stupid. Thor is a male god from Æsgaard. If he is "unworthy to wield Mjölnir", it simply passes to another who is. If this is a female, she is [her-own-name here], goddess of Thunder and not "Thor". Sif is considered "worthy"? Sif would be the new goddess of Thunder. She wouldn't be Thor.
Otherwise, it's like saying Emmitt Smith gave someone his number 22 and now that guy's "Emmitt Smith". Stupid. He's DeMarco Murray and he's awesome in his own right. Even took his own number - 29.
Does Jim Carrey become Loki if he puts on "The Mask"? Wait... bad example. Actually, The Mask merely amplified the wearer's tendencies toward chaos - didn't make him Loki.
As for Loki himself, does he become Odin when he steals the throne of Æsgaard? Nope. He takes on Odin's appearance, but he's still Loki.
The call rings far and wide for "female leads". Well, Ms. Marvel has had her own comic over the years and that could be brought back. Spidergirl (Peter Parker's daughter) had her own mag for a while - why not put her back to work? Black Widow would be awesome in a "spy thriller" type of story line. Imagine if Marvel decided to put Natasha and Elektra into a storyline together! Oh, the head-butting we could see in that one!
Peggy Carter could be a fascinating World War II story! The creation of S.H.I.E.L.D.? C'mon! Bring it! World War II? Any day!
Thundra and Tigra have both had short-lived solo adventures as has The Wasp and Valkyrie. Spider-Woman (Jessica Drew) had a longer lived title through the '70s and into the '80s. She-Hulk? Great character. Put her name on a few issues and you'd get some readers.
One of my favorite comics (DC or Marvel) was Dazzler. I know there are a lot who don't think so, but she was one I enjoyed - personal opinion.
The problem isn't that "Marvel doesn't have female leads or titles", the problem is that they fail to provide the gripping stories and substance that makes their (Marvel's) male characters so endearing. Maybe it's because the Marvel writers have been almost all male and just don't relate to female characters.
And, I don't think Marvel has a shortage of "minority titles and characters". Black Panther, Black Lightening, Luke Cage, Shang Chi... they're there - problem is hiring writers who can relate to those environments and cultures.
I don't see any reason to "reboot" a comic book character other than for "natural" (aging, died, disillusioned, etc) reasons. Marvel is usually pretty good about doing this. The "Thor" thing, though?
I don't think so...