It's definitely looking fishy.
The SATCOM pings sent out by the plane indicate that 5 hours after the plane switched off its transponder, it was cruising at its normal flight level. And the military radar which tracked the aircraft, tracked it following several 'waypoints' on an air route heading west, before losing it again. This points to deliberate pilot action. Even if it was just following autopilot, somebody would have had to program that course into it, as it's not the course it would have normally followed.
There are two types of radar, primary and secondary. Secondary radar works using the transponder, and gives details about the aircraft as well as its location and height. The transponder was switched off to evade this type of radar. Primary radar works like a ship's radar, in that you don't know who each contact is, but you know they're there. In the local area, the primary radar had a range of 200km, but the military radar had a longer range and so tracked the plane further. If the plane had come close to shore pretty much anywhere else in the world, the likelihood is it would have been picked up, unless it was shadowing another aircraft by practically flying next to it, which is incredibly difficult in an aircraft of that size.
The evidence points to the aircraft being deliberately flown to an alternate location. But the main question is where? There's a lot of places you can get to in 5 hours and 40 minutes at 500 odd mph, but very few places that you could do so without detection. If it has landed, it would certainly have to be covered up, possibly at a governmental level, and this is incredibly unlikely.
The aircraft was carrying 227 passengers instead of 243, which indicates a heavier cargo than normal. Could someone onboard be trying to steal it (if it was anything of value)? It's not unheard of for gold to be transported on commercial aircraft, or more sinisterly, weapons. But that's very unlikely.
All this sounds very tinfoil hat brigade, but it does raise questions.
I personally think that the pilot and/or copilot have tried to divert the plane to an alternate location, for whatever reason, and never made it, possibly by running out of fuel. It would certainly take a knowledgeable person to fly outside of radar detection for 5 hours, especially if they were anywhere near coastlines.
I feel desperately sorry for the passengers' families though, it must be a horrible feeling being, similar to losing people at sea.
Flight 19's wreckage has never been located by the way, several planes were found but they were later proven to be part of a dumping scheme.