On the one hand, I am firm believer in "never say never." There have been too many aviation accidents where observers say "No pilot (or crew, or aircraft) would ever do that!" - only to be proven wrong when the final report comes out. Pilots and planes sometimes do the craziest things.
I do have doubts that a crew would attempt to complete a 550nm flight if they had bounced the engines on the tarmac on take-off, but you just never know.
I do have doubts the impact mushroom cloud would have been that large (see end of final glide video) if the fuel tanks were empty, but you just never know.
For the moment I lean to the theory of - ground contact during gear-up touchdown (intentional or not) - followed by mechanical engine failure due to ground contact (G forces, inner inlet shrouds dislodged, fan strikes, oil loss, etc.) - followed by attempt to stretch glide at alpha-floor (which rarely works, but if the alternative is hitting a 5-story concrete building head-on....?).
Will stay tuned for further information.