I watched the podcast.. I found it pretty normal. He doesn't come across as unstable. They are basically discussing technology and related things at an intellectual and philosophical level (one could say geeky). Elon states that he's not a business magnate, or whatever wikipedia says he is, and that he's an engineer. His day to day is solving engineering problems. His tweets are a distraction, probably regrettable and play out of his limbic system.. the adage that you should not tweet/email/post when drunk, high etc... we see that play out everywhere. My take on why he got involved in the submarine thing was because it could be viewed as a hard engineering problem that they could help solve... even though the situation didn't necessitate new equipment per se. He's got a team of crack engineers and wants to use them to solve problems... much like Tony Stark. He wants to fix LA traffic which is unfixable unless you dig tunnels. Basically a bunch of smart engineers solving problems outside of the box.