There are actually a lot of new units coming on the market soon. This article from August claims there are twice as many units "in the pipeline" as the number that made it to market in the past decade:
I'd guess that there are NIMBY building costs that prevented housing construction until the rent got so high, but it does look like an end is in sight.
There is a lot of focus on Ellis Act evictions, but the fact is that there just aren't very many of them. This article claims only 116 in the last year, which is significantly less than the numbers 5 or 10 years ago:
The solution to the rising price to rent is to increase supply. Anybody in SF should be able to drive up Market and see evidence of the massive number of units just opening up.
http://www.socketsite.com/archives/2013/08/all_48000_san_fra...
I'd guess that there are NIMBY building costs that prevented housing construction until the rent got so high, but it does look like an end is in sight.