That's why tourists, who will spend 8 hours a day in the saddle, use either drops or trekking bars overwhelmingly.
In the states, probably. Elsewhere -- hell no.
No, this product is going to be aimed at older cyclists with fit issues, and following a Rivendell-style fit with a nice wide drop bar will solve their problem much more satisfactorily than simply rotating the bar backwards.
I would see this marketed to a lot of the newer "fitness bike" people entering the hobby at present -- think of all the hybrids and flat bar road bikes flying off the shelves right now.
All being able to raise the stem does, IMHO, is rest one's back.
Not in mine. I don't get back problems, but I do get some wrist and hand pain on some rides. Also, headwinds -- or when I'm entering the city so I could see better.
To me, the question would be how reliable is it when exposed to the weather? The other is how do you get this down to a price that people will pay? Yes, old grouches and people who are already happy with their set-up won't care -- that's obvious. Honestly, I wouldn't need one either. I could just see a market for a neat idea, that's all.