There would be room at add content as part of the up coming expansion that only unlocks at a higher difficulty. I just think you have to be careful that you don’t create the opposite situation where the ‘restricted’ area is the only optimal way to enjoy the open world in the end game.
To me there is greater room to expand on the concept of Capstone events and named boss layers. Even strongholds could be retain on a weekly timer and respawn at a higher tier of difficulty.