In my mind, as far as conspiracy theories go - and assuming this is a conspiracy rather than an accident - I would think the only justification for hijacking the airplane for something onboard would be if it was very large. My reasoning for this is that it would seem to be much easier to acquire, say, a laptop with classified or proprietary data on it a number of different ways than to take out an aircraft for it. I would hypothesize that it would have to be something far more difficult to acquire through conventional schemes that was in the belly of that plane. Maybe gold, maybe any number of things.
However, I can't rule out that there is the remotest chance of a controlled landing in water. I know this is a low likelihood, but it's not unprecedented in the least. Saying, for a moment, that this was the case then it is feasible that there would be little to no debris field and the plane sinks. I really don't think this is the case because at the very least it's highly likely the plane would break up as it sinks and some kind of debris would make it out - such as luggage.
Then again, if it were a suicide mission he could have simply nosed down into the ground (i.e., 911 Pennsylvania flight) and leave a relatively small scar that may escape notice.
While on a much, MUCH, smaller scale, consider how much debris has not been found in the search for AE's plane. Sure it has been over 70 years and of course people living on the island likely appropriated any usable debris, but you would think that there would be something - especially and not in spite of 70 years passing - as the plane continues to disintegrate underwater. Understandably there have been pieces found that may be debris from the Electra, but all the scouring of TIGHAR over many years has produced very little. So, even on a scale of 100 times this, the possibility that debris has yet to surface isn't that far fetched.
This all leads me to believe that, really, anything is possible and nothing can be ruled out until some evidence, any evidence, surfaces.
In the end, we all know what is going to happen here. 70 years from now Ric's great great grandchildren will be running TIGHAR searching for the mysterious MH370 flight. They will be on MALAY-XXV, their 25th mission aboard their hover boats looking for signs of the crash. It will end up that there was a mysterious settlement deep in the Indian ocean on a remote island that prospered for a time during the 21st century who made interesting art from aircraft aluminum and sold it on eBay. In the end all the passengers booked the flight specifically to escape society and it was all quite logical. The only difference being that THEIR ROV worked....
On an unrelated note - this is my first post, do I REALLY have to do FOUR verifications to post a comment here each time?