Looking at it again, a bit closer, I'm pretty sure it's Monica Rambeau in her Captain Marvel costume.

I see three possibilities for the introduction of mutants, the one in the quote, they're from another universe where they've been around openly for ages, or something happens that suddenly turns people into mutants. The last one seems like the least likely to me since there are so many mutant characters with histories going back decades or centuries before the comics. It's going to be kind of hard to do characters like Wolverine, Magneto, Professor X, Destiny, Mr. Sinister, or Apocalypse if mutants are just being created when they're introduced. The Sherlock Holmes characters are public domain in the US, right? So if they do Destiny she could be Irene Adler?25M mutants took nearly 40 years to get to in the comics. I’m sure that the MCU version will start with the mutant population being significantly lower. And in hiding due to racism, which will be retconned (like Wakanda) as always a thing just never relevant to any onscreen adventures so far.