Several chocolate products in the UK seem already to have done the foam trick (add air), particular ones like Thorntons (individual chocolate box chocolates). You can only do that so much though. They used to be one of my favourites but now they're more like mousse than anything, the mouth feel is very poor and the flavour is greatly reduced - adding air with individual wrapped chocolates works commercially because they don't have a weight marked on them.

Cadbury, trimmed bars using carefully designed shapes (rounding off corners, adding curled edges) that seem as big; also adding cheap filler like popcorn or puffed rice.