I know they did so far, but as they wanted to extend the engine to support whichever graphics API the end user desires, I guessed given the formulation that Sid used it could be possible they implemented a parallel DX11 render path to test if it works.

EDIT: Heavily unrelated question, in one of the first posts here in this thread Sid had given an example on how to set up a custom application using Rayne; The process did however not include setting up an explicit program entry point (a main), but instead providing an ApplicationCreate function which instantiated and returned a child class of RN::Application.
Am I right in assuming that you guys actually hide the program entry point within the engine library?