You gotta ask yourself a question - what is in it for the company that must maintain the infrastructure? $25,000k per year is a drop in the bucket.
Second is the question of security over open airwaves. IMO, I don't think WIFI crypto schemes have reached the level of maturity where the general public is going to be open to sharing their connection with perhaps hundreds of users per node, each transmitting sensative material (maybe).
Third is the question of bandwidth - WIFI right now is line-of-sight. In order to make it reasonable for the end-user, the signal has to have sufficient strength to go through walls, etc - and unless you have high gain antenna's slapped all over the place, esp in the major metro area - I just don't think the technology is mature enough to allow it.
To answer yr timeline question - if a company were to undertake this - best guess - 7 to 10 years if there were public support. But that is really the driving factor - the Cali folks saw the need - and had the desire - and for their demographic it worked out in their favor.
Wolfala