i tend to favor vacancy tax, but this won't fix the problem with developers. SF needs to reform their review process. this is TLDR but there was a big study about this: https://www.nytimes.com/2023/10/25/us/san-francisco-housing....
it's already incredibly expensive for a developer to even go through the review process for a development, let alone build it. a vacancy tax would further deter developers from building in SF (as it's already happening due to the terrible review process)