Any engine itself creates higher layer for coder and it’s made for you so no need to care about those APIs and concentrate on gameplay code and content, thats one of the point why developers do Engines first. Renderer plugins suppose (as there always be some diffrences) to be seamless, work the same, behave the same and most impotently look the same and your gameplay code should work the same regardless of renderer used.
Mac already using OpenglDrv renderer and as you see no body discussion much about it other then prefermence 
So at most what you will be dealing with in this topic is profiling for specific renderer and hardware, but as i know Unreal partly do that for you too