Track maintenance is the single biggest cost sector of rail lines in good condition even on very low slopes. The ballast needs regular inspection and replacing even without adverse weather or underbed problems, and the track can develop cross fall or slew and/or creep in transverse and longitudinal directions over time, sometimes taking subsurface layers with it. Every other kind of gravity storage makes more sense on paper than this, even the tower crane rearranging concrete cubes proposal.
It's true that track maintenance is costly but it's mostly costly because there's a whole lot of track to maintain; many hundreds of miles of it, often in hard to reach areas. This looks like it'd be a few hundred meters at most, all parallel to each other in one place. So hopefully it's easy enough. The tower crane also requires maintenance.
