This kind of thing could be done by adding intermediate "goals" into the Raids/duties/etc.

For instance..... a "serious" party should be able to take down a given boss in a shorter amount of time than a casual party.....so gate the option for more difficult content there....

If the party is better at the game and its mechanics, they could get the option to "take on additional enemies" or "increase severity" etc..... If the party is not up to task, not geared properly, more social or casual in nature, they take the regular path and aren't even prompted for the additional difficulty.