I agree this would be very handy. I am not sure though if it's possible. It could very well be though, I know ffmpeg can inject certain metadata such as titles but I don't know if it can inject the whole spherical data thing.
Although, there is a python API for Minecraft and there is a python script to inject the right metadata into a video file so that YouTube can recognize it as 360. Perhaps someone with more brain cells than me can put the two together and automate it. Perhaps, it could even be built into the mod directly. The devs would need to comment on that though.