Spoke to the engineer.  He is going to run some fea on various options for increasing the compression and sheer properties of the foam.  Once he has done these, I will make some samples to validate his numbers. 

Using glass between planks/panels would be hard to manage, but cool if it could be done without adding weight (ie, no overlaps).    Using foam with better properties, or timber stringers between planks/panels would be quite simple.  All of these, with light laminates wpould probably show up as print through over time.  Not a big deal, more something to think about as you are turning expensive filler into dust and respiratory problems to achieve a perfect finish.