According to the World Health Organization, the rate of suicide in Malaysia is close to the lowest on the planet; a tenth or so of rates in European countries.
This, plus the fact that in every picture you see of either pilot, they are smiling, and not forced smiles, but "I'm so happy, I can't help but smile", smiles, are two reasons I lean away from pilot suicide in this case. But, you never know. If I had to guess, I think it was a fire, that may have done damage, resulting in crew and passenger incapacitation or death, then burned out, leaving the aircraft to fly until it ran out of fuel. The "facts" used to debunk the case of a fire may not be any more accurate than the "facts" the Malaysian officials have changed from day to day. BTW: I take back my qualified "some Asian countries" remark. Even qualified, it was far too sweeping. I stand corrected.