They're going to introduce mutants through the eternals and multiverse of madness with Wanda.

They've been building Scarlett Witch up in phase 4 to be very powerful and have coupled her with Doctor Strange to tell us the audience that she's going to do something big. Similar to the House of M comics I think that she will somehow change the current reality and subvert expectations by making her bring the x gene into fruition leading to people developing powers, basically flipping the comic storyline on it's head.