I see Musk has decided not to join the board of directors. Not enough info for me to discuss what that might mean, other than the Twitter CEO sent some internal memo out about people on the board of directors having to "work in the best interests of the company".
Maybe Musk decided that would constrain him too much. Or maybe he's just gonna sell all his shares this week and make a few billion in profits.
As a director, there would be some kind of constraint limiting him to some arbitrary percentage (around 15%, IIRC) of ownership. By not joining the board, he can buy as much as he wants.
Also, that announcement from the CEO mentioned something about directors having a "fiduciary duty." Basically, that means directors are supposed to do what's in the financial interests of the shareholders, not rock the boat. Taken together, those two factors wouod significantly tie Elon's hands if he really wants to upset the apple cart.