WSB, from your article:
"The share of empty homes that are for sale rose to 2.9 percent, the most in data that goes back to 1956"
"The vacancy rate was 3.5 percent in urban areas and 2.6 percent in suburbs, the report said."
It won't take long for even 1% growth per year to wipe that out. Great Britain just recently started monetizing their debt, and the Fed will consider that in their meeting next week. If so, that will create jobs here that will attract immigration from countries where they can't do such blatent monetization because it would be a more immediate disaster.
As you point out, some of the vacant houses are in locations of such little value that they are demolished. The movement from rural to urban areas passed the 50% mark, but is still continuing, leaving shacks like the ones you see sometimes on
http://www.lovelylisting.com/. The US population is also migrating west, leaving large urban areas in the Northeast and Midwest such as Detroit as ghost cities. The driver's license for Feb is out, and it shows that while people didn't move in to Washington as much as before, there were leaving at an even lower rate, so the net gain is still almost the same.