I agree with Passenger 389
Most likely scenario so far is that a disgruntled pilot with a psychological imbalance has tragically decided to exit with an enormous splash.
The fact that the final ping is recorded extremely close to the temporal fuel endurance of the aircraft might strongly suggest the aircraft was flown until the fuel ran out. It is also easy to speculate methods in which the only person on board who was alive for the 6-7 hours was the 'hijacker'! That being the case it is not a huge leap to speculate that the intention has always been to make the wreckage of this aircraft as difficult to find as it is possible to imagine. That also explains the erratic flight path. I am so sorry to say this, but perhaps this aircraft will never be found.
Truly terrifying 'terrorism' indeed! Cruel. Evil.
So if you wanted to 'hide' the end, would you take MH370 over land, or over thousands of miles of remote, deep ocean? (7400m in places!) Where surface debris has already had a week to drift unnoticed.
Of course, the intention could have just been to show up the talking head idiots, for precisely what they are! And my goodness haven't we had plenty on this one!!!
Finally. If this is just a one off, it's bad enough. It also makes a total mockery of security checks for pilots, since they are the only ones on board who don't NEED a 'weapon' (read nail file!!) to take over the controls! Better to give pilots more psychological checks. Perhaps akin to the screening received in Israel before every flight.
However if this isn't a 'standalone', another hijack, using a related method could have a similarly devastating effect on aviation as Sep 11th!
Worrying times for all.
Sincere condolences to all concerned.