Overall, the design plans exceed my expectations, and I really hope that they come to fruition. This article, however, mentions that there will be some kind of internal streetscape:

Glass covered streetscape: The area between the seating bowl and the outer buildings will be covered by glass to create a “covered via,” or interior streetscape, filled with trees, retail, dining and other amenities. Bridges and walkways will connect the outer buildings to the seating bowl through this covered interior street.

Christopher Ilitch, president and CEO of Ilitch Holdings, said the covered via will be open year-round, not just on game or event days, and could play host to a variety of daytime or nighttime events. Like any good urban street, it will be designed to be walkable, with flexible programming, and to be “a very festive area. ... The net effect is a very energetic, very exciting space,” Ilitch said.
This is a bizarre element to include an otherwise very urban-friendly plan. The "indoor via" sounds to me like an indoor shopping mall made to look like a street. While this could be fantastic in the winter, it will either [[a) take people away from the actual streets outside, harming the atmosphere there, or [[b) end up mostly empty on non-game days.

On the whole, though, this is a small concern because the plan sounds great.