Elon Musk’s floated merger of SpaceX and Tesla would do more than unite rockets and electric cars. It would fold two of the world’s largest corporate Bitcoin stashes onto a single balance sheet. Speaking on SpaceX’s third-quarter earnings call Tuesday, Musk said the boards of both companies had formed special committees of independent directors to weigh a tie-up, cautioning that treating a deal as “a certainty” would be “overstating it.”