might just have a point...
We've had stacked wafers for years, but the issue with them is loosing heat as they tend to bend when getting hot, causing problems with the contacts between the layers and thereby limiting the speed you can run the components at.
My guess is that the novelty they are trying for is the 'flexible plastic pcb' (aka 'flex') which might be better at keeping in contact allowing parts to run hotter and therefore faster. I guess the issue then becomes the thermal conductivity of the 'flex'.
I'm far from being an expert about these things, so someone will probably chip in an tell me I'm all wrong.