It's beginning to look more and more like possibility (1) doesn't -- pardon the expression -- hold water. Per NBC News, citing Reuters:
Military radar evidence suggests the missing Malaysia Airlines jetliner was deliberately flown west toward the Indian Ocean’s Andaman Islands, sources told Reuters on Friday as mounting evidence pointed to a criminal inquiry into Flight MH370.
Two sources told Reuters that an unidentified aircraft -- believed by investigators to be the missing Boeing 777 -- was following a route between navigational way-points, indicating it was being flown by someone with aviation training when it was last plotted on military radar off the country's northwest coast.
But terrorism doesn't make a lot of sense, either. Given that the destroyed plane was going to disappear into a large body of water, possibly not to be found for years, terrorists would presumably have either radioed in about what they were doing, or else had someone on the ground prepped to claim responsibility early enough to be convincing (like about the time the pilot stopped communicating by radio). The point of terrorism is to incite terror, after all. Not terror of accidental crash, but terror of hijacking and murder. If that's what was going on here, the terrorists didn't do a very good job.
The third possibility that I haven't heard mentioned anywhere is: Theft.
A Boeing 777 goes for $250-300 million dollars new.
For obvious reasons, it seems like it would be difficult to sell the thing whole, but maybe someone figured they could knock down a few million by selling parts to airlines under the table? Land the plane in the equivalent of a stolen car chop shop, kill the passengers and make bank.
Or ... perhaps theft pursuant to terrorism. Maybe a week or a month from now, the airplane will appear somewhere unexpected, in the guise of another scheduled flight, and swoop in to knock down a building.
Yeah, it seems far out. But the whole thing is getting pretty far out, isn't it?