> What if automation and robotics made homesteading much easier, and more likely to succeed on land that was previously considered useless?

Then that land (if not already privately owned and actually available for homesteading) will be homesteaded, privatized, enter the land market, and not be rent-free land that is available. Just like the land that was attractive for homesteading in the past has been. Sure, its a one-time land-rush just like the initial homestead act, but after that the same forces of centralization of property that always work in a capitalist economy will work on it.