> If Carousel is intended to solve a user problem, neither I nor other potential users seem to be able to figure out what it is.

> users don’t seem to be keen on replacing the main Facebook app

> a sufficiently vague target is harder to miss

The common thread between these products is that they are solutions in search of problems. Great design can't help you find the "problem" to solve faster than any other technique. This is a product/market fit article that just happens to focus on design driven products.