There are aqueducts between the CV and coastal areas. The water goes the other direction.
If desalination becomes widespread, I imagine the water not shipped to the coast could remain in the Central Valley. I don’t know one way or another if this would make political or economic sense.
Water rights are so complicated that they’d probably sell the water to the Central Valley before it ships to them. I think it very unlikely that they’d give them up.
There's no way the water would be affordable for agriculture if it had to pay for pumping it uphill/inland. There's a reason the rivers flow in the other direction.
I wonder if NIMBYism blocked that?
And if an agency wanted to transport water like the USA national oil pipeline system, would they be blocked similarly?