Just look at the line in Google and in various publications/articles. It strikes me as a smaller-scale Southern California analog of NWP (flame bait!).
I don't see San Diego needing or wanting to pay for a *modern* railroad on that line - would cost far more than the traffic is worth. However, if the Mexicans go ahead with one or more of their port schemes on the Baja coast for intermodal or general/bulk freight, they will need rail connections. That's where the upgraded line will come from, if there isn't a better route that's all-Mexican to the UP at Calexico or Yuma.
San Diego doesn't have the port facilities or reasonable places for inland transport by rail needed for a major intermodal port. For now, they're naval and autos and bulk - and will likely stay that way. If SD were to actually develop significant intermodal facilities, they would have their lunch eaten by LA/LB and, in a few years, the eastern ports after the new Panama Canal opens. Better to concentrate on the specialties they have now - for which they're in better shape than, say, Eureka because they actually have an active economy (based on more than controlled substances), an operating railroad (LOSSAN) and decent freeways.
If you want to run a slightly cartoonish version of it in MS Train Simulator or Open Rails, a route is available at Trainsim.com and at [
www.silogic.com].