When using ES3.1 and Multiview for Gear VR, scene renders black (although it could be ES3.1 and not multiview issue)
When using ES2 and Multiview option, performance is significantly lower than without Multiview (59.xx fps vs 39.xx fps).
It also seems that MSAA is not working at all with Multiview enabled. Here are 2 screenshots taken on the device:
With multiview: Google Drive: Sign-in
Without multiview: Google Drive: Sign-in
(you can see aliasing on the arrow and on the floor rubble tiles)
cool, except that report doesn’t even mention AA issues.
since TAA is not working with Mobile HDR enabled, I rejected the tests.
MSAA works on mobile VR. TAA never worked and it’s not the best AA method for VR anyway.
Apparently Multiview is not designed to work with ES3.1 per Oculus (due to drivers on the phones) and it’s not production ready for ES2 either. Maybe in UE 4.99 … err, nearest future, it will get better! 
For me the bottom half of the screen is fully aliased while the top is clear.