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.