Something about the flight path, and in particular the slow, smooth but unstoppable right roll several seconds after the fire's peak, says to me "fire damage to wing hydraulics > uncommanded asymmetrical flap retraction on starboard wing."
Rather like American 191 DC-10 at Chicago, only flaps instead of slats.
Can't be confirmed or denied by the video alone - too low a resolution (plus the wing and engine are out-of-frame several times due to camera wobble).
If I'm right (and that's a big IF, of course) I expect the tin-kickers will probably find some clues in the remains, and as a test flight, the aircraft was likely wired to the gills and there may be data that survived.