One thing I noticed from that video on Pocketslider is the camera appears to be able to go in one plane only ie. Either left or right OR up and down, depending on which rail it's attached to.
Now to my mind, the clever money is in a vertical rail that moves along the X axis so the camera can track in 2 directions at the same time. Obviously that requires a stiff Y rail plus heavy duty X motor OR a small pocket size camera or a Square frame so the Y rail has support top and bottom and thus the duty requirements of motor and Y rail are decreased.
However, achieve X & Y movement, and an infinite number of camera positions are possible only limited by the area encompassed within the length of the X & Y Rails.
It also opens up the possibility of computerised tracking if you want to go to the next level and have the camera follow a pre-defined path over time.