This will have some effect in San Francisco (some neighborhood development plans and zoning regs are so low density all projects require approval). But a lot of projects (like "the monster in the mission" to replace an old Burger King and empty warehouse with housing) would not be able to be blocked under this law. They follow the existing development plan so they require no exceptions.

Even out here in Sunset, all the land is zoned 40ft or 60ft. If you include a basement, thats 4-6 stories when most structures are 2. If you weren't subject to massive delays and reviews, it would certainly be profitable to tear down some of these single-family homes and build 4-6 story apartment buildings.