hahaha, so just bad timing on my part eh?
Yeah, that's an issue with all apps that can open on the request of another app...frankly it's why I almost always choose the "just once" option, just in case, because you're right, it really is a pain to unset -- there isn't even a mapping like you'd find on a windows machine of file type to app, you have to actually go find the app in settings IIRC and clear its mapping. Bad design when it's bad, extremely convenient when it's good (mailto opening your email client, for example)
Anyway, that's a bummer, skybox is definitely the best VR video player I found. I even paid for VRTV just so I could have something semi-good for now, but it's not as full featured as far as I could tell.
For your development efforts, I'll tell you my use-case is Plex. Plex doesn't give non-root access to mobile-synced files, so unlike say, Emby, I can't just go into the app's data and pull a file in, I have to use the open...is it called 'intent'? It's been a while since I've done Android dev...
Hope the feature comes back! Maybe put a notice in the description or something? Don't let the bad users ruin it for the rest of us! :D