What I'm thinking it would be like, is kinda like Menyoo, where you have lists and settings to use and you can replace the character(s) with any character you want. You select the Cutscene you want and it shows all the characters that can be replaced with the characters in the database, and the camera pans around to the character that you want to replace and it also shows the character that will replace them and maybe, you can also edit the vehicle, change color, upgrades, and cosmetic stuff, but not replace it, the Cutscene would break if you could replace the vehicle, I think.
An example of this would be, in Fame or Shame, Instead of Michael, Trevor, Jimmy and Amanda being in the Cutscene, it's the Mp Male and Mp Female characters in the Cutscene. Or it would be cool to see Michael, Franklin, and Trevor alongside our Mp Character in the Doomsday Heist Cutscenes, like it was going to be in the cut content.
Another reason this why this would be a good mod to make is because it would be an easier way to create our own stories with the Cutscenes and be cool to view them as other characters.