It seems to me like they are simply showing off the new map pack and the new September update at the same time. The 'mythic' below halo could have simply been added to tell people that it contains the mythic map pack, and it may need to be running on the latest version for those maps to work.
Yea, I don't think it's going to be a hardcore expansion. It's probably just a special version for development purposes.
I think this is what they needed to do to make some new stuff. I hope that it's like a really big expansion that fixes a whole lot of crap. It would be owsome. Thanks for finding. Love, Zachary9990