Difficult to capture reflections across a large screen while also dealing with outdoor lighting, glare, and moisture. The touchscreen part isn't usually what makes outdoor signage expensive compared to IP65, temperature control, and a secure housing, all of which would still need to apply here.

This looks like a neat option for retrofitting, and I suspect it'd work for some non-screen glass applications too. A combined IR/visible light solution would be interesting too, since I suspect those are complimentary (IR touch has issues with radiant light, while this wouldn't; this would have issues with low/no light, while IR wouldn't).