The big showstopper is what to do with the hypersalinated byproduct. You'd kill anything that was near where it's let out. It's also very corrosive and I imagine the would be a problem moving it far from the plant.
It's not actually that big a deal, it's just they don't want to deal with it. You discharge pipe has to be a lot longer, spreading it over enough water for it not to matter. (Spread it enough and it's no more of an issue than evaporation at the surface increasing salinity.) You can also pump ordinary seawater into the discharge system to lower it's salinity before release.
If you have the real estate you can also go with evaporation ponds. Probably not too viable in California but it could be done in Texas.
If you have the real estate you can also go with evaporation ponds. Probably not too viable in California but it could be done in Texas.