There are a few problems with that plan.
1. What will California do with the concentrated salt discharge from the plants? Just wait until there are a few dolphins floating on the ocean to see how long the plants run!
2. Where will the large amounts of required power come from? California is already "living on the edge" every summer. The NIMBYs (not in my back yard) stop every attempt to build power plants in CA.
3. If the NIMBYs don't want power plants why would they allow desalination plants right on the coastline? The plants would have to be built on the coast to minimize pumping costs and electric consumption.

We already do this, it's called bottled water.

But seriously, "the coast" doesn't want treatment plants, or the associated power plants, in their backyard. The complainers are called NIMBYs (Not In My Back Yard).

California NIMBYs even want to control the type of power plant Nevada has in its backyard!

The Governor's suggestion to use desalination as an option is one that is under consideration. However, the point of the pipeline to provide an option to the Colorado River, which is drying up!
There are at least a couple of major problems with desalination:
1. It takes a lot of electricity to operate the plant, which is in short supply in southern California. Southern California doesn’t want to build power plants for its own use, so why would they want one to benefit Nevada? If NIMBY, or Not In My Backyard Yard, prevents the construction of more power plants why would they also agree to the construction of several large reverse osmosis (RO) plants?
B. The plant produces a concentrated salt waste stream that must be dealt with. If environmental approval can be obtained the salt could be mixed into waste water and dumped into the ocean. However, what happens when it is shown that the concentrated salt killed a whale, or dolphins or the lesser spotted purple snail?
RO is a solution but there are challenges to making it work. It will not work for Nevada if the Colorado River is dry or if we waste it.