So far I've identified:
1. Commercial real estate. Could take a short position on any public companies (ex. CBRE) though they're likely too diversified to drive them down to zero.
2. Hiring. Could bet against LinkedIn? Most local recruiters / agencies are privately owned and the public ones are diversified.
3. Ancillary services. Seems like start-ups serving start-ups so there's no publicly available position to take.
4. Tax Revenue. Assuming a contraction, can you bet on local municipalities being short on budget / revenue with a smaller tax base?
Might be a fools errand to short these if the excess capacity can be picked up by all the behemoths (Google, Facebook, Apple).
I wouldn't dare take a short position on SF residential real-estate although outlying areas might see a larger contraction.