My initial impression was that it's pretty nifty and fun to watch but of questionable value other than perhaps removing the need for a frame. But I wonder if there could be multiple print head sets on the same rail, each with its own filament, making multiple color or multiple material prints easier to achieve. Going to another level, multiple rails, each with multiple print sets could enable even more materials and colors. Coordination with each getting out of the way of the other would be an issue, as might be stringing and cohesion between differing materials. Still it's an interesting development with some great possibilities.
I do love the motion of it, despite the preposterous cantilevered wiggle waggle it would have. The algebra of the inverse kinematics must be something else. I wonder how many degenerate rail positions there are for an XYZ...
Would a circular track function? It might have some added benefits