I think it's more likely that some of these franchises just stop. Marvel is continually introducing new standalone movies to the cinematic universe. If every character continues as an unending franchise they'll soon need to be releasing a movie every month! Iron Man might just stop, as we see new trilogies for Captain Marvel, Black Panther, etc.
Alternatively we could see Marvel attempt to bring some of it's new generation from the comics to the big screen. The Riri Williams character could take the mantle.

Disney seems willing to push the diversity envelope in it's core releases and it could cross over into the Marvel Cinematic Universe as they have a truly global and diverse audience to appeal to. I'd be very excited to see something like this while at the same time dreading listening to the "It's just PC BS" backlash.