I'd actually like to know more about this point as well.
There seems to be two main arguments about seller's market/highly-priced markets in general: one is "buy low/sell high" and another is "this trend is going upwards, and so one should follow the trend until there are signals that state otherwise."
My current belief which is subject to change is that the fact that a market is a "seller's market" should not in itself determine whether prices are "too high." Of course, a market could and would fluctuate between a buyer's and seller's market so you could arguably say that you ought to wait until a buyer's market to buy. However, there's no guarantee how long that would be (or at least, I don't have enough knowledge to know--if you know, say, with good evidence, that 2 years from now the prices will drop significantly then waiting is prudent).
If there is no real evidence of large, detrimental economic factors going on (war, people moving out of the Bay in masses, an unusual amount of new construction making the supply on houses extraordinarily large for a prolonged amount of time), then there is no reason to assume that the seller's market will swing back to a buyer's market any time soon.
The fact remains that the population in the Bay is growing year after year, tech companies are still expanding (to such a point where they are closing down Gold's Gyms, grrr, but that's another story), and this is still a highly desirable place to live. Fundamentally, to the extent of my knowledge, the Bay will still thrive and grow for a long time to come.
But the question of: "Is the cost of living in the Bay so high compared to the rest of the country (maybe historically, or just the affordability index) that it is now a very attractive option for a ton of people to start moving elsewhere? How high would prices have to go for that to happen?"
That's a question I don't know the answer to. NYC has done pretty well for itself and the Bay certainly has a possibility to end up like that, but one could also argue that the Bay and even SF in general has a lot more to do to make transportation as efficient as over there.
I'm kind of rambling and going off topic, but basically I guess what I'm trying to say is: a seller's market does not guarantee that the price will go down any time soon, nor does it guarantee that price wouldn't crash any time soon. Fundamentally, there are more important factors to consider, and the fact that a place is a "buyer's" or "seller's" market ought to be a supplement to an investment decision, rather than the overarching point of contention.
But anyway, I'm doing out-of-state investing for right now because I don't really have nearly enough capital to do investments here.
PS GO BEARS!