It's my understanding that courts have actually allowed municipalities to use eminent domain (condemnation) to take private property (paid for pursuant to certain standards that are *supposed to* reflect fair market value, only to turn the property over to private sector interests so they can build their mall or whatever, create jobs and build the tax revenues. I think that sucks, but I think it has been upheld in court.
As to corner crossing, it may be political suicide but I'm all for it. There may be litigation but I think the land owner would lose. I also think the fair market value for a few square feet of land would be chump change. Finally, this would be WAY better than some legislative alternative that purported to allow corner jumping without paying just compensation for the "taking" in, what I believe would be a violation of the 5th.
So, yeah, the states should condemn and pay for access. I think it should be limited to the width of a person walking, and not include cars, 4X4's etc. But that's just me.
Edited to add, I know Wyoming has a law allowing a private party to condemn access through another private parcel to access his own land. It has to be the least imposing route, etc. and it can only be done if there is no other way in.