Viewing Octane renders on GearVR is incredible. I don't know of any other device that matches this experience at the moment. You can view your pano renders on other stereo HMDs, but I think it is hard to settle for anything less than the experience we get today with GVR.
We are planning to submit the viewer app to the Oculus store. It turns out we can't just post an .apk here or on Google Play, as Oculus requires the apps to be signed by them.
The lua viewer is meant to serve as a preview tool so you can quickly test renders on GVR. Since it is lua driven, it can also be expanded with new features via ORBX lua packages (similar to script nodes in Octane).
Regarding hostpots in the viewer, we are implementing this for the WB project, which is a navigable VR experience, with story, intro and audio. The entire package is saved as an ORBX file with lua controlling navigation, menus and more that can be loaded by the viewer. Authoring something like this is not yet exposed directly in Octane at a high level. Down the line, we'd like to properly support exporting navigable ORBX+lua packages directly from Octane for viewing on VR/AR, Web and mobile.