My experience is that there isn't a market for these units. A project on 24th St. languished years ago, Frank Norris didn't fill up very quickly either.
It reflects the aging staying at home even when they are alone and living in a family home that should have been listed and sold to a new family a decade ago. A long time SF Realtor said once that San Francisans don't "move up" they add on or get carried out. It rings true to my experience.