Other than RDJ, I think other actors could step in. I was more along the lines of the era of just fun MCU movies. Homecoming with the annoying MJ character was the first warning sign.
Not sure when CM was tagged as the future. Did that pop up just within the last year? If CM is a hero with no weakness what drama is left for the MCU? Honestly Black Panther would be a better leader of the next stage of the MCU.
Marvel tried pushing the Inhumans to no avail, and Captain Marvel is their newest “You will take this character and you will like it” push.