I understood what you wrote and I had experience with both Faceshift and other facial tracking softwares…
Currently, if you’re familiar with C++, I guess that since Faceshift is capable of streaming data via a network you can stream data to UE4 and connect the various blend shapes to a rig inside UE4, but until now no one did it.
Well, you asked for facial tracking, now if you need to move from Unity to UE4 just for that I suggest to give it a couple of months for the plugins to be available and check the results by yourself.