The game already HAS "timed quests", and in one of the most insidious forms as well: you just trigger timers by proximity without even noticing them or being told about them.
Once the trigger is activated just doing a rest or changing zone translates in automatically failing a chance to get/complete a sidequest.
I wouldn’t mind if they changed the format of those. I am not sure how many world events there are, but so far I either haven’t failed any or failed some without ever knowing they existed.
But no, let's freak out about "limited time" instead.
Always!!!