It allows for as little as 5%. Some in the city are fighting for more. For example Jane Kim, the SF supervisor who Bernie Sanders just endorsed for state senate, is fighting for 25% (down from 30%).[1]

Basically this state bill is a developer move to undercut SF's negotiating position, as they have more political influence at the state level.

[1] http://www.bizjournals.com/sanfrancisco/blog/real-estate/201...