There are two groups who might embrace a folding helmet design, that I can see. One is the person who rides to transit, but doesn't want to leave the helmet locked to the bike, exposed to the elements. The other is the frequent bike share customer.

The issue, though, as others have pointed out, is that this design does not appear to be very compact when folded. I would think that in order to gain appreciable acceptance among any population who might want such an item, the folded size would need to be a real space saver, and probably more important, the folded shape would need to conform to commonly carried bags (purses, briefcases, messenger bags, etc...). My sense is that this design remains very wide. perhaps if it folded the other way, so that the front and back collapsed, and the sides were more static, making a longer, but narrower 'package'.

I would probably buy a folding helmet for my bike to transit days, if the design were actually space saving. Oh, it would also probably have to come with some sort of protective case, I think.