Part of me wonders if it isn't a side-effect, but the goal: put the squeezin' on the shorts. But, man, if that tin-foil hat theory is true, Musk better have someone in the wings at least pretending to want to finance this lest the SEC come a-knockin'. Normally, I'd just pass that off as "haha, wouldn't that be funny!", but given some of Musk's tweets lately, there's still a little part of me that entertains the idea as plausible.
Yeah I'm really wondering whether this was legal - I would've been on his ass if I were the SEC for illegal price manipulation. Even if he doesn't go through with it, it's still bumped the stocks up by a lot. Could've been a move to scare off the shorts?
By the time you had made your post, Tesla had already issued a press release saying the same, and news had come out that Musk had been talking to the board about it for the past week. So, yeah, he was serious and not being manipulative, and AFAICT completely legal.
Until Tesla's economics become obvious to all in the market, this is probably the best decision; this allows them to be more focused on the long run.