This is what's happening in Chicago right now. Single family homes and two story apartment buildings, which dominated Chicago and made it a pleasant place to live (lowish density, lots of room, decent sized backyards, etc) have been replaced in gentrying areas with super dense condos that are 3 to 6 units large on the same tiny lot. No yard, no parking, no front yard, tiny bedrooms, etc.
It really changes the character of the neighborhood and the system really can't handle this kind of density. You would have 3-4 people in a SFH which is now a lot with 6 condos with 18-24 people. This means not only higher pricing but more traffic, no parking, higher load on utilities, local parks being overfilled, etc.
No one talks about density it seems, but something very real happens when we quadruple density like this.