Anyone else get the feeling that we're never going to know the true cause?
Not me. The cause will be found, but first the aircraft or wreckage must be found. In spite of all the tongue in cheek space alien Twilight Zone references here, I think those are just from people frustrated by the lack of data. Both inside and especially outside this forum, there are a lot of highly intelligent, capable, talented, and experienced people working on this; and they won't stop until they find an answer. I'm also sure that assets we can't even imagine are being brought in by various intelligence agencies.