My experience so far with Gear VR has been that you can do up to an hour and then get tired of it or need to take it off to re-orientate, I'm sure this is different for everybody.
I think a key to get the experience right, while VR is still improving is to blend the two mediums, i.e. have a game/experience where you do stuff normally but need to go into VR to perform certain actions. This will help with adoption.
Is there any way to do this in Unity where I can prompt my player to put on the headset and it will seamlessly continue my game into VR without going through the Oculus or whatever other interface?
i.e. Connect to game as a user, game prompts you to don headset and as soon as headset is donned, game continues...
It is not yet possible to dynamically switch between VR and non-VR in a single apk. However, you could ship 2 apks and send intents between them to get the same behavior.