Great news, official Google Cardboard support seems to be coming to the engine!
See here: https://www.reddit.com/r/oculus/comments/4iq3rq/androidvr_likely_to_be_announced_next_week_at/
It looks like the existence of a new “AndroidVR” (Google Cardboard) plugin was leaked in the breakdown of the latest 4.12 Preview 3 release notes.
This note has since been pulled.
It is slated that the Google Cardboard SDK will be relaunched as AndroidVR this coming Google IO.
From the looks of it, AndroidVR looks to be a collaboration of sort between Epic Games and Google.
Best,
Minxies