My understanding about 111 Main (and someone correct me if I'm wrong) is that the building will actually be supported from the roof. In other words, structurally speaking they will be 2 separate buildings. I would assume this is so that they didn't have to engineer the EPAC to be a Theater AND the base for a skyscraper.
To me, this would make sense why we are yet to see any steel structure growing outside the core, even though the steel at EPAC appears to be topping out. And would also explain the reason for the slow pace of the core, as it needs to be strong enough to support a majority of the weight of the building.
Just my 2 cents though, and I may very well be wrong. However, if I am correct... I think we got us 1 AWESOME!!!! Tower coming to SLC's Skyline.