From what is in the public domain, it appears the only source of information being used to define the search area is the Inmarsat data. The problem with this data is it generates a multitude of possible solutions, resulting in an enormous search area.
If the current search does not turn up MH370, we will need to either accept it is lost and move on (which would be deeply unsatisfactory), or else accept that the Inmarsat data alone is not sufficient and employ alternative methods to find it.
I believe MH370 was most likely a criminal act - that is, the plane was deliberately diverted, and then flown under human control with the intent to make sure it was never found and would disappear forever. There is a fair bit of evidence that supports this theory. So perhaps we should consider MH370 a criminal act, assume the motive was to minimise the chance that the plane will ever be discovered, and follow that to its logical conclusion.
If you wanted to make a plane disappear, the deep south Indian Ocean is as good a place as any. And you would hope to end the flight in a way that minimised debris.
If you accept the Inmarsat data, then there are two possible scenarios:
1. A flight south with autopilot engaged, fuel exhaustion,
and crash - likely with much fragmentation and debris.
2. A flight south under human control, fuel exhaustion, and possible controlled ditching with somewhat less fragmentation and debris.
From a Bayesian perspective, the lack of any
debris whatsoever would seem to increase the probability of the second scenario. The lack of debris also favours a location further away from land.
If true, this supports a plan to take the plane as far as possible in an unexpected direction and avoid it ever being found. So perhaps Thomas Bayes would now suggest we look for the furthest SW point along the 7th arc consistent with the data. Further, should we look at the various unknowns and now input values (or scenarios) that would achieve the goal of the most SW point (i.e. the most remote location).
Coming back to the earlier phases of the flight. Many have speculated that the pacs were turned off to incapacitate the crew / passengers. Time of useful consciousness for non-acclimatised people at FL350 is perhaps 30-60 seconds. There was some talk about a possible climb to FL430, but I don't recall if this was ever verified.
There has also been speculation about crossing the peninsula at relatively low level. Again I don't know that this has ever been verified. This hint at a low level flight might be a convenient excuse to explain away the very limited primary radar data after the transponder ceased operating. I wonder however if the plane really did cross the peninsula at a low level. There are several reasons why the "perpetrator" may have *not* wanted to descend:
1. Although sudden depressurisation at FL350 will reliably incapacitate people, it won't be immediately fatal. For a period of time, this incapacity will be reversible and people will regain consciousness upon descent to a lower level. The best way of ensuring no interference would be to keep the pacs off at high altitude for a significant period. Certainly while crossing the peninsula. The last thing the perpetrator would have wanted would have been for someone to make a call or text from the plane. I am not saying that such a call / text would have been possible - just that the plan may have been to ensure it was impossible. In addition to phones, there are other potential ways a passenger could cause interference. There would be no way for the perpetrator to know that an off duty pilot / engineer was not a passenger.
2. Less chance of an intercept by a military plane. Again, it is fairly unlikely this could have been achieved even if MH370 had been low level. But high level makes it even less likely.
3. A low level flight would burn extra fuel which would limit the final leg south.
So if we assume the plane didn't descend to low level crossing the peninsula and if we assume the pacs were kept off for a significant period of time, how much would that increase the maximum distance the plane could have flown by the time of fuel exhaustion? For the same endurance (i.e. the time of the final 7th handshake), fuel not burned crossing the peninsula at low level would have allowed a higher speed and a more southerly course to reach a point further SW on the arc.
The other piece of information that may be useful is the location of the solar terminator at the time of the 7th handshake. The terminator was some distance to the west of the current search area at that time. In order to have any chance of a semi-controlled ditching and minimising fragmentation and debris, the perpetrator would have needed some daylight. West of the terminator, the flight ended in darkness. East of the terminator, the flight ended in light.
So I would favor a location near the 7th arc, slightly to the east of the solar terminator at the time of the final handshake. This location would assume a higher speed (or a more direct track) than has been assumed thus far. Again, maybe there was no low-level flight across the Malaysian peninsula, and instead this fuel was available for a higher speed / greater distance south.
In short, I suepect the perpretator wanted to get as far away from anywhere as possible. I believe the plane had the fuel (and the daylight available) to go a bit further SW than the current search area.
Why would someone want do this? There are lots of possible reasons.
1. It has already become one of the greatest aviation mysteries ever
2. It has successfuly embarrassed Malaysia on the world stage
3. China is the country that makes Malaysia most nervous, and the country that Malaysia would wish not to upset. Most pax on MH370 were Chinese citizens.
4. If we didn't have the Inmarsat data (and the perpretator was likely not aware of this), then we would be left with the following. An almost certain knowledge that the plane was stolen. A vague prrimary radar track heading WNW into the Indian Ocean towards various unfriendly places. And a plane with the range to reach them. That scenario would have been deeply disturbing to many governments and intelligence agencies.