I have operated SIN LHR for the last few years routing over KL, Port Blair then over Calcutta. The new info about this flight being flown over this similar route makes we wonder if it "tailgated" such a flight heading towards India.
SQ068 was discussed earlier as such a possibility but nobody was ever able to confirm its routing on the evening in question. This is clearly not an amateur operation and that might be quite likely. Coupled with the US General stating that the flight's destination was Pakistan would also compute. Beyond Pakistan, they would start running into some very sophisticated US Military kit, both on the ground and in the air so Kazakhstan seems less likely?
That asssumes the NW track, which would logically be more likely in the case of piracy. IMHO, that is less likely than the SW track, more likely in the event of a suicide mission by a party or parties unknown and for unknown reasons. The US has already deployed assets to the IO and, I'm sure Submarines will already be lurking thereabouts also.