If MH370 did turn left and head west into the Indian Ocean , and if there was evil intent , it certainly had fuel to reach Diego Garcia (much the same distance as KL-PEK) and I am certain the US has both on island and space based surveillance assets to keep a very close eye on any unknown vessel or aircraft approaching this very important and rather secretive base.
Might explain why US seems to be going along with the 'it turned west theory' without being too specific about why they might support it. Picking a flight full of Chinese passengers is hardly likely to lessen any tensions of something bad did happen either .
Also I believe the India military are pretty concerned to protect their sources and resources in the Andaman islands which they see very much as an eastern frontier of India for maritime purposes.
Whatever happens I can see a mandated introduction of GPS location reporting for all long haul aircraft relaying constant position reports via a secure sat comms link with no access or control function from from flight deck