We have been considering going down that route and releasing Diffd as an open source project while offering a hosted version that is the easiest way to do thing

We have been considering going down that route and releasing Diffd as an open source project while offering a hosted version that is the easiest way to do things in parallel and across multiple browsers and operating systems. However, we expect that initially most will add Diffd as a manual step at the end of their pipeline. So, it's not like their ability to push code is completely dependent on a third party, it's just another check. Taking a dependence on Diffd is going to be less risky than depending on a third party for your CI server like Travis CI, CircleCI or CodeShip.