Dumping 200 million tons of new "solar salt" on the market would collapse prices and signal the end for the existing player in the salt industry. I don't think this would be an issue in the long term as salt derived from a hypothetical mass-desalinization industry is essentially free. Replacing heavy industry with the byproduct of an essential and beneficial process is the very definition of economic and environmental efficiency.
California gets a secure water supply, consumers and industry get cheaper salt, and the imprint of the salt mining industry is no longer a concern in the environment.
*Source: http://www.saltinstitute.org/salt-101/production-industry/
http://www.wbez.org/series/curious-city/how-much-road-salt-e...
Obviously a little drive, but salt prices are high up here ;)
To supply 10 million households with drinking water from sea water, then, produces 200 million tons of salt. The current global salt market is 250 million tons, at a price of about $50 / ton. I find it unlikely that the market would bear dumping that much salt on it at a price that would make producing the salt worth it.
Disposal is probably a cheaper course.