jonb: I think the continued pinging for 7 hours also discounts the theory that the plane landed intact somewhere, as presumably it would have kept on pinging.
With the current information would the most likely theory be that it ditched in the Indian Ocean. Hopefully Australia has some primary radar capability extending into that search area to prove or disprove the potential southern track, and India has some primary radar from Andaman Islands or the subcontinent to pick up a trace on the western track.
(Edited)
Assuming it landed somewhere why would it keep pinging after the aircraft was shut down.