@AB - I don't think you can make that conclusion. PVC vs. PU is a matter of having a ski with dimensionally identical cores, with laminated fiber product and resin wrapping it. In the hollow skis, there is still something inside. In the case of AM I think what they were doing is assembling a ski rather like a boat is made.
Your boat has an outer hull, inner webbing "stringers" and then a top deck.
I think the AM ski is an outer lay up forming the bottom "hull", a "stringer" system instead of a core, this stringer provides the mechanical/structural element, and the design of the "stringer" gives you most of the mechanical properties of the ski, and then a top deck.
A foam core you have the same system, but the "stringer" is the core, and you cannot modify the performance of a solid foam core that is machined in the same way that you could a matrix of carbon.
That is atleast how I think he is building the ski, until someone mails me a hollow AM to cut in half on my bandsaw....
Also I think if you take a chunk out of any modern ski, you probably don't want to patch it up with some bondo and take it back on the lake.