"Nowhere to go but up"? How quickly we forget the last housing bubble. If the price of housing goes up faster than the salaries of the people who want to buy it, eventually we'll get to the point where demand will drop sharply: someone with a $100K income and $100K in student debt just won't be able to get a mortgage for a $2M condo. As demand drops, housing prices will drop, and people who bought into the market at…
The mid-2000's housing bubble was characterized by rising prices and rising supply. The SF area housing supply is artificially and stupidly constrained by highly restrictive popular regulations in the bay area. There is no reason to believe that it will suddenly collapse, because people actually need these homes and not because they're making trying to flip it to a bigger fool. Nor can they build new ones (which would undermine the price floor).
Even if all those regulations were to suddenly go away all at once (wouldn't that be nice?) what you would probably see is gradual price normalizing over many years and you would probably still ultimately end up with a price level above normal.
In a bubble the price collapses all at once from speculators all trying to dump the asset that they didn't even have any use for otherwise, but the people who had been buying the asset before were other speculators who are now also trying to sell, so you see a sudden market collapse. Speculators know this so even the expectation of a market downturn can trigger the collapse. If people actually need the homes they aren't going to try to sell them the moment they see or expect the market to soften, precluding a such a momentary collapse.