Nvidia has added support for eGPU over TB3 (and TB2 i guess) in 361.75.
I just tried and it works for me! (2013 rMBP 13" + Aikitio Thunder2 + ASUS GTX 970)
There is a new UI in the latest drivers that shows what applications and games are running on the eGPU.
And a "Disconnect GPU" button that I have not tried yet. (I'm guessing TB2 hotplugging on Macbooks still wont work in Windows)
Edit: found a thread on this here: https://www.techinferno.com/index.php?/forums/topic/9289-optimus-now-works-in-win10-using-36175-driver/
Edit2: I played a bit with the "Disconnect GPU" button. I think all it does is disable the GPU in device manager. It switches to "Connect GPU" after you press it, but the problem is after you reboot, the nvidia drivers wont load and you have to enable the GPU in device manager.
Also, physically disconnecting and reconnecting the eGPU does not work for me without a reboot, but I think that's a problem with Macbooks on Windows. But disconnecting works fine.