I think Morrowind handled optional content well.
Basically, in Morrowind, you are expected and even directly told to go explore, level up, get stronger, etc., before tackling the main quest.
Without doing this, you won't be strong enough to complete the main quest.
So, you go and get stronger, level up, etc., and then start the main quest later. The tasks get even harder, so you may need to take a break again to level up more before finishing things out.
In this process, you've done a lot of the side content simply to get strong enough to handle the tough main quest, get the good items, etc.
So, if all of that content was simply optional, there wouldn't be quite the importance given to it to actually complete it. You could just blow through the game basically.
So, we'll see how it turns out. Just because I disagree a bit with the philosophy doesn't mean the game won't be good.