I'm not understanding how it breaks the API. I believe I've kept the same defaults for `replaceRightViewController:animated:completion:` and merely added `replaceRightViewController:animated:animationType:completion:` as an additional way to access more specific functionality.

Basically, in my app I use fade when I'm transitioning between similar items (e.g. detail view controllers for items in a table view controller on the left) but what essentially is a pop and push at the same time when you're switching to something completely different. (Push and pop at the same time meaning that you maintain the idea of a stack by popping the right view controller and push a new right view controller in the same animation.)