aaannnd,
socketsite jumps in
I'm still going through
the official SF Planning doc (277-pg PDF), but one thing that jumps out is that in 2010 they decided that developing the space over the railyard would be infeasible (sorry SPUR), since there would be no space along the edges to put activating stuff like retail, or even the means (escalators etc) to get up to the developed part. so the 2012 version of the study assumes
no surface railyard, and considers redevelopment from a clean slate, either with existing freeway or new boulevard. whoof.