What is the affordable housing solution in U.S.?

[Phil C.]

Have heard a lot discussions on the affordability of housing in U.S. They pretty much tells the same story. 

On the supply side, the newly constructed apartment buildings will be built to serve the high end market due to the cost of construction, the desired return of investments, etc. Even class B and class C buildings are currently experiencing renovation to pursue higher rent by the value adding process. 

On the demand side, the median income level does not increase much. And the income gap between rich and poor is getting wider. More people will tend to rent for longer time due to various reasons. 

This trend posed a serious problem for the housing market: who will serve the medium / low level demand  while the supply moves away from them? Will the high end market collapse at some point due to too much supply?

How do you think?