Halo Open World Rumors Appear Online

Is a Halo Open World coming as the next new release title (Not Halo 2 Anniversary)? That's the latest rumor circulating online thanks to an industry insider named Ahsan Rasheed who is usually quite busy at every E3. In one of his recent Twitter posts, he had this to say;
 

So what to think of this? We have already heard other rumors stating that the campaign could be up to 5 times longer, and now this? The knee-jerk reaction is are they trying to copy Destiny in an attempt to take away some of their steam?  Another thought is this has indeed been a long time coming since it had been talked about as far back as Halo 3 if you've ever read or listened to any developer commentary.  Mainly in the expansion of each map as technology improved over time. 

I think it would be great as I was always frustrated with being confined to a certain area during Halo Multiplayer and even certain Halo Campaign Missions. The only question I have is was this decision made early on or has it been made recently and would it be a hack job that might make the game suffer?  Would it be better to wait to implement for a future Halo game?

Thoughts? Could you imagine Masterchief roaming around GTA style smacking Grunts?