[ardecila]

A) Office uses can certainly be concrete construction and probably will be in this case
B) views command a much higher premium in the residential sector than the office

If your framework is Chicago, then much about this project doesn't make sense. The Chicago market is highly specialized and competitive, and different sectors are on different market cycles - it's highly unlikely that a developer would compete well in the office and residential and hotel sectors all at the same time.

However, in a healthy smaller market like Minneapolis without a lot of new supply in any sector, mixed use towers can be a way to diversify and reduce risk. If the office portion fails to rent, it can always be converted to a different use, etc.