Yeah but that doesn't happen in TW2 or Skyrim or ME or DAO either. I understand what you are saying and I agree that time is an element I'd like to see in games. I think it would do a lot for replay if there are 80 hours of side crap but you have 40 hours to finish the game for example you would have a nearly whole new game second time through. It also would mean that your character would be making choices about what he felt was more important to do as a side item for example.
Realistically though people don't seem to generally share that view because they want to leisurely wander the roads and pick weeds or drive lousy moon buggies around looking for rocks.
Yeah, that would be pretty cool, limiting the proportion of the game you have time to do in a single playthrough. I've had some similar ideas buzzing around in my head for a while. Unfortunately, it's unlikely to be implemented as, not just would a lot of people object, but the majority of players don't replay games, even BW ones, so there would be a lot of "wasted" dev time.
But I don't neccesarily think things need to go that far to better integrate the open world and the main story. It's not so much about limiting how much exploration people can do, or where they can explore but when they can go exploring. Take my current playthtough. I've just unlocked the second part of "Here Lies the Abyss", having spoken to Hawke's warden friend. I've been told that the wardens are partaking of a ancient blood magic ritual, likely under the influence of Cory. I've been told where this ritual is taking place. And I've been told when it's taking place: immediately. At this point, if I want to save the wardens, exploration makes no sense what so ever. If I go off exploring for a while before heading out to the Western Approach, then, according to the story, it should be too late. The wardens would be bound by blood magic to Cory's pet demons. The only way to save the wardens should be to go there immediately.
However, once I've addressed that particular immediate threat, the game should then not straight away give me the next main plot. It should be uncertain where and when Cory is going to make his next move. And that would be the time for me to go exploring, while the Inquisition, including you, are looking for more information on Cory's plans. While from a pure story perspective, the amount of time to explore should be limited, I would have no real problems letting people have as much freedom they like at this time, at least until you unlock the next part of the main quest in which something that requires your input is happening at a set time.
It's about allowing the player freedom when it makes sense for them to have freedom, and restricting freedom, or at least having negative conseqeunces to it, when it doesn't.
DA:I's flaw in this respect is that it utterly fails to integrate the main plot and the open world. The main plot continues itself regardless of the open world - as soon as you complete one part of the main quest, you're given the next part, without any real need to go out into the world except for the arbitrary "need X power" - and exploring the open world makes no sense while doing the main plot as the events of it are supposedly under time constraints that you can't control.