1. Given the obviously high degree of precision in planning the operation. one would think they would have been at least able to come within proximity of another plane, if not carry it out successfully.
2. If that was there intent, unless they were targeting a specific flight to intercept, why head into the Indian Ocean? Far less traffic there, than over the South China Sea.
3. All airliners gave the automatic collision avoidance system..which warns if another plane is on a collision course. I think it only functions the forward 180 degrees, so to achieve surprise they'd have to overtake the plane from the rear...much harder to do, as speeds are pretty much the same, making closure far more difficult.
With regard to collision avoidance systems, I believe they are dependent on each airliner having their transponders on.
“However, there are a few problems with it, just off the top of my head.”
Not too mention the DOZENS of available targets, at that time, on the same very busy airway they were on.
TCAS works 360 degrees.