If a Tesla-SpaceX merger is in the plans, China can prevent it unless Tesla gives up the Chinese market, half its size, and becomes a regional car manufacturer.
Mercedes and BMW are finding out that the Chinese are pretty much done with foreign prestige brands. Elon will have to find someone willing to buy a falling knife.
Or he could buy a US mobile network operator. That almost sort of makes sense. Elon could slash the workforce and turn in a couple of years of good numbers before things fall apart.