red herring
I'd be very cautious of giving too much credibility to the "stan" theoretical route. I guess that the Malaysians have chucked that in to counter Chinese criticism of the search so far. Any route from Gulf of Thailand to the stans would take the a/c through Chinese airspace or at least radar cover.
Also - a few home truths about the stans from someone who has travelled and worked in all of them over the years.
Pretty much all are ruled by anti-Islamist (though obviously Muslim) dictatorships or autarchies, who are mostly desperate to bring their countries into the international community at some level.
Geo-strategically they are beholden to and dependent on Russia and China.
Defensively they all use Soviet-era kit, and have large defence forces and good radar cover. It is unlikely they would allow penetration of airspace by an unidentified aircraft.
The only significant US-related target in the Stans is Manas airbase in Kyrgyzstan, which is scheduled to close in July 2014.
I assess it as extremely unlikely that a 777 could be brought into the Stans without being identified and probably intercepted; and impossible (not a word I use lightly) that any state actor in the region would encourage or tolerate such an act.
Also, before we get too excited about Uighur seperatists in Xinjiang, the Chinese have the place under almost complete control. If they allowed (or failed to notice) a hijacked airliner to land within Chinese sovereign territory, the repercussions internally would be inconceivable.
The only possibility with the so-called "Northern route" that I can see is that the aircraft was intercepted and destroyed or forced down in NW China by Chinese air defence. There are huge areas (look at the Takla Makan desert on GE) where this could be effected without attracting too much notice.