I wrote the guys at intelligent assistance, I think it can’t be done as of now:
“I can see part of the problem. When you import the MP4 to FCP X it does not read the metadata from the associated files into the MOV that FCP X wants for this type of footage.
When FCP X ingests the GoPro footage from the cards, it reads the timecode from the associated files. While FCP X will read the mP4 directly, it loses all the associated metadata, resetting the timecode.
Premiere Pro handles this metadata in a different way than FCP X. FCP X cannot read Premeire Pro’s method, but Premiere Pro can read FCP X’s method.
If you imported the media to FCP X from the original card, it would be rewrapped to a MOV file format (FCP X’s preferred format and to which is rewraps almost everything on ingest, wrapping in metadata with it.) Then I think FCP X will have issues reconnecting as it is expecting an MP4 and it will have a MOV. It won’t like that and most likely will refuse to reconnect.
Abut the only suggestion I can make is to ingest the material into FCP X from the original cards, then have Premiere Pro reconnect the project to that new media. Then do the XML translation.”