Musk isn't crazy, but he certainly isn't a stickler for rules, either.
In my opinion, stock markets are one of the worst innovations in the history of economics because they pervert your core business from "making money" to "making people think you're making money." Things may have been different before Welch and "shareholder value" but that predates my investment experience by decades. Either way, the logic of taking things private makes perfect sense to me - tire-kickers don't get to tell you what to do, assholes like Carl Icahn can't swoop in and upend your business model because they have sand in their vagina, and you don't have to report shit to no one. Considering SpaceX isn't modeled after Boeing or ULA but after the Korolev Design Bureau I certainly see where he's coming from on the whole "gone-private" thing.
Is he serious? Damn skippy. Will he get away with it? Less certain. I've been hanging onto a few shares since...err... March? Which means I think I'm in at about the same strike as you are. I'ma ride it out 'cuz the crazy fucker is approaching profitability for the first time and having worked for public vs. private corporations the private ones are hella more efficient. Maybe the asshole will even hire a designer. I mean, it breaks my heart that he bought a fuckin' McLaren Mk I but his cars look like the default avatar from a generic Korean sedan appreciation forum.
Anyway. According to the WSJ the SEC is now sniffing around his anus about those tweets but I really doubt Elon Musk gives a fuck what the SEC sniffs. If he can get away with it he will. And in order to get away with it he need only prove he had an investor at the time of the tweet who told him they'd finance the thing at $420 a share. He doesn't need to prove they weren't lying, he doesn't need to prove they didn't do it so they could scoop up a bunch of shares prior to the announcement and then dump them immediately after. I'll bet he does it.
PS. Thy banjo? 'tis dope.