This is ENTIRELY speculative but in the comments regarding the Sunset District's development plan revisions, some chatter here for a possible alternative to 80+ years of major commute traffic along 19th:
http://www.socketsite.com/archives/2014/08/blueprint-san-franciscos-sunset-district.html
Historically, the non-upgraded portion of Route 1 from Font Boulevard to Lake Street (19th Avenue, Crossover Drive, Park Presidio Boulevard) was to have been part of the original pre-1968 proposal for Interstate 280. There also was a very brief concept in 2001 for tunnel upgrades for Route 1, Van Ness Avenue/US 101, and even the Panhandle area, though that never was taken to a serious level.