If you have a problem related to GDK - i would wait for 5.7. i was looking through GameInput files commit history and found this :
https://github.com/EpicGames/UnrealEngine/commit/65c84cca5d42682b4bf71644165dd4ed31b42838
Hopefully it means GameInput would just work in 5.7 without us having to do anything special. (launcher version, no GDK requirement etc)