How about converting glass/steel skyscrapers to malls or department stores (esp. for higher cost goods that are best not to have at street level), while converting many of the smaller office spaces that can qualify into housing? Most of the stores from space-wasting ground-level shopping malls could relocate into these spaces, for the most part. That said, parking areas (or a large part of them) would have to be converted to loading areas I suppose, so stores would have to offer delivery for larger purchases.