Agreed that it's moving down the value chain, many other open source projects out there doing similar things. There's also Tyk Open Source API Gateway (https://tyk.io) and API Umbrella (http://apiumbrella.io/), and APIAxle, though that's been around for a while now.
Also API market is intended to grow to $660 million in US by 2020 and over a billion worldwide (http://blogs.forrester.com/michael_yamnitsky/15-06-07-the_ap...). So it's definetely not small.