Should do like old console games back in the day did. Sure you can play on the easiest difficulty, but to access the post story content you have to clear on the normal difficulty.

So until you clear msq on normal difficulty you can't enter the current expert roulettes, 24 man's or raids.

It's only fair to the players who did complete it on normal to not have to be forced to group with mouthbreathers who can't clear the already faceroll easy msq solo instances.