What is so odd about this story is that all plausible theories assume a perfect execution of a well-engineered "plan". The longer such a sequence of "perfect" executions needed, more unlikely that theory should be. So, a plane landing undetected in some "stan", requires such a long sequence of correct execution with a combination of evading detection knowing radar holes in multiple countries, fuel planning, navigation, etc., that such an event would have to be highly improbable (not to say impossible).
Consider even simple things like the transponder being switched off before the last ATC communication (there is some ambiguity here as to whether the transponder was switched off or just the ACARS which is more difficult to do). Whoever did this if intentional would have to know exactly where the prior radar coverage ended and the next coverage started (which is possible for a pilot regularly flying that route) with that ATC since otherwise, the communication would have been a bit different than a normal hand-off. The timing of this seems to indicate a perfect execution of this without a large margin for error. This is likely in isolation but adds to the sequence of events that all had to be done like clockwork to achieve a destination in Asia or Europe.
Even the theories for a drastic altitude changes (if the data is correct) seem to assume a perfect execution of an intentional plan (incapacitate the passengers, save fuel, avoid detection by shadowing, etc) with an extremely low margin of error which makes such a sequence of perfect executions even more unlikely.
The point is that such a long plan is very difficult to pull off intentionally and so very unlikely.
What is missing is a theory that what happened was consequence of one or more plans gone awry (for example, the climb to altitude was an unsuccessful attempt to detonate an altitude sensitive explosive in the cargo as the final goal). As you can imagine, this is almost impossible to do given the realm of possibilities without much information on the intent and actual actions and why the reality after the fact turns out to be such a different situation than the theories.
It one were to argue on probability of execution alone, it is likely that the plane really didn't get too far from the last point of contact (or went in a straight line) and crashed intentionally or otherwise somewhere in the ocean that has not been searched yet or difficult to search in.