The X-Men and Fantastic Four can officially join the Marvel Cinematic Universe now that the Disney/Fox deal is done, but that doesn’t mean it’s going to happen anytime soon.
That means those characters can and will eventually join the MCU fold.
The MCU has largely succeeded through careful planning, with the ability to be flexible.
[Then] ‘How can we introduce new characters that even hardcore fans, comic fans, have barely known or barely heard of.’