Why would this ever be a smart move? Afaik he couldnt realistically dodge more taxes than he lit on fire at Twitter.
AFAICT, it was very nebulous at the time that it ever would be a common holding company for those (and Musk’s other companies), and very good reasons were cited for being skeptical that that would be workable. And, to my knowledge, none of the other companies has been put under X Holdings.