I hear that pressurization isn't a problem since the sub itself is at a normal (atmospheric?) pressure, unlike a diving suit.

Hearing about how many fail-safes the sub had, including one that would go off even if everyone was passed out, yet there is still no sign of them. I can't help but think it was either destroyed on the way down or got stuck on something. I also think the decision to paint the sub white was a huge unforced error. There is also a chance that they DID make it, we just haven't seen them.