That would be awesome!! I use mine in the field for data collection and for my work the GPS accuracy is good enough, but I do have access to RTK if needed. It would be interesting to compare.
As far as I know noone has successfully recorded external data into the GPMF of GoPro videos. I think someone made some progress in the scuba-diving space, but not sure how far they got. I think it's not worth the hassle, recording the data externally and syncing it with the video afterwards is easy enough.
I haven't got my GoPro yet so haven't anythign to compare, but once I do I'll have a look and see what the difference is, if any. I'm sure data can be manipulated afterwards to ensure the accuracy is what i need. Accuracy becomes infectious after a while!
For my aerial photo/video work, I have been using the $229 SolMeta GMAX logger which shows camera orientation, and has a more accurate barometric altimeter. That may be directly connected to a Nikon camera, in which case the Exif data is written directly to the image file. The logger also records a downloadable log of the unit movement on 1 Hz interval.
