Post-ARR is in a difficult place because "less important parts of the MSQ" may still heavily involve characters who will not be available later, or need to move to a different location. It's why the hard mode trials are required rather than optional.
Even if you could turn MSQ quests into sidequests easily, they still need to be rewritten to remove the links that tie them to the quests before and after them, and those quests rewritten to ensure the join is seamless.
