I assume it to be satire. The idea of using prison labor that is then released has all the signs of an emotional trigger for both sides of the political spectrum. I am surprised he did use migrants caught attempting to cross the boarder in exchange for citizenship.
Conceptually it is interesting. The discharge from a desalination plan is ecologically troubling until it is diluted, but it is not really HazMat. In theory you could remove the salt using evaporation and sell it commercially. Salt is recovered this way in many desert areas. The space needed to do so will be huge and the process is not very efficient even if you used solar power to preheat the brine.
Ultimately, I agree that the Little Pacific Project will quickly be proven impractical (if it was even a serious proposal to begin with). But considering that the long term alternative is a mass migration out of AZ, NV, southern UT and most of So Cal, we might find the impractical bar to be much higher than expected.
Unless there is a change in weather patterns over the next several years, areas that depend on the Colorado or are pulling water from underground aquifers that are being depleted, could find gasoline prices cheap compared to the per gallon cost of tap water.