If Musk is serious, he'll work to get candidates running in state and local government elections, building up to running candidates for federal office. If there's no grass roots to build up a party, it'll fail. He has to have an infrastructure and support from below to create anything higher up--politics is a house of cards and if there isn't a foundation, there's no win possible.

It's the same reason Bernie Sanders would have had enormous problems as a president. He didn't have a constituency inside government willing to take tough votes and advance his agenda. He would have been an army of one, which is a recipe for being ignored and overridden by Congress.

Third party?  Sure.  Musk as de facto leader?  Hell no.

The problem with a third party run by Musk is that it would just be young dudebros and Republicans running under a different name.