Elon Musk isn't really interested in Bitcoin if I should say so, so buying the number of Bitcoin to rival that of Satoshi will just mean he wants to do that for publicity stunt and nothing else. Satoshi will keep increasing in wealth because Bitcoin will keep surging. Now that Satoshi is in the wind, we can't speculate if they would add to their holdings but for the time being, I think the title of biggest Bitcoin holder would still go to Satoshi Nakamoto.
How do you know that he is not interested in bitcoin ? Do you have exact idea of what exact coins he is holding ?
Think back to the last three years. Musk is currently one of the most disliked figures among cryptocurrency investors. Even Trump is more popular; he can at least provide support to investors and have a positive impact on prices. Musk, on the other hand, is not. People no longer want him to talk about cryptocurrencies and are uncomfortable with it.
When bull season comes, he starts talking, makes money from it, and then sells everything. And then, lo and behold, he stops talking at all
