i think the adaptative difficulty aproach is an interesting one , but it requires a lot more time for design thinking from the gamedev to adjust internally when the player its having a rough time playing the game , resident evil 4 its a masterfull example of doing that , you can look at some videos explaining it .
also in general terms i think it depends on the style of the videogame for having an normal, adaptative or optional difficulties, the optional ones are most apealing for action or arcade style games i think.