It's an interesting solution to increase the supply of housing in areas that are already (relatively) dense and unaffordable, like the Bay Area, where it's already common for people in downtown areas to live above or adjacent to retail businesses, and where many people consider walkability to retail businesses a valuable thing. Santana Row is already designed and targeted at high-end tastes for retail, so it's easier to extend that to high end housing.

However, in suburban areas where housing is cheaper (per sq ft), unless denser housing at the mall provides other urban-style benefits (i.e. higher end retail, easier workplace access, mass-transit hubs, shared civic spaces, cultural event proximity, etc.) it may just appear like "living at the mall", with all the connotations thereof. Put another way, all else equal, most people don't want to live adjacent to the "Hot Topic" and the "As Seen on TV" stores. The balance has to be more toward feeling like a place to live and work, not a public shopping center. Dense cities, with all of their retail, still feel like places people live and/or work.

If, however, they are able to provide those other "public" goods along with the mall, then perhaps it is a great shortcut to reshaping the landscape of suburban america towards a more mixed-use and sustainable model.