…to be self-evident:

If it performs wonderfully on GearVR:
then it will be a dream on the Oculus Rift,
and take little or no effort to port, other than input harness*

If it performs adequately on the Rift + PC,
it may or may not work well on GearVR.
In fact, it may take both a massive re-factoring as well as a
total re-thinking of graphics, models, textures and code.

Conclusion?

Be smart : Mobile First.

Develop for the Gear. Port to the Rift. WIN.

* a few words on input harnesses:

Designing input mechanisms for the GearVR touchpad is a tricky business… its a VERY limited input surface, and we tend to use both gestures AND a lot of “gaze detection” combined with taps…

for the Rift, we often take the easy way out : keyboard input. At dSky, we are especially fond of the following, which are easy to “find” for “blind” VR users:

• space bar (easiest to find… big and central and edge)
• cursor arrows at lower right (2nd easiest to find blind)
• ESC key (far upper left, also “feelable”)

Truth be told, we should ALL be designing for
a) gamepad, and
b) natural hand tracking devices,
c) with keyboard as a “fallback”
d) oh, did i fail to mention the venerable mouse? ooops!

as the long-term goal for natural and intuitive VR input streams.