Both the U.S. Constitution and the California Constitution contain special protections for private property rights. What you're describing--"requir[ing] access"--is a property right called an "easement." The State cannot "simply modify the rules" to give itself a property right that didn't exist before.
There is a constitutional way for the state to acquire a property right against a property owner's will: eminent domain. But that requires "just compensation" (i.e. California will have to pay Khosla for the easement). California is hesitant to do that because it would rather try to bully Khosla into giving up the property for free.
They should eminent domain a teeny narrow strip right across the center of the property, and try to get it assessed as pro rata on acreage. Maybe two very narrow strips in different places for one way traffic in each direction.
That would be a perfectly reasonable and legal thing to do. But California doesn’t want to set the precedent of having to actually pay for property rights. Ever since Penn Central gutted the Fifth Amendment, states prefer to use regulation to take private property for public use.
If the state wants to modify the rules after the fact, they typically have to provide consideration for that. This plays out all the time with imminent domain. Otherwise this is a plain and simple taking.
