Disclaimer: I don't have a clue and nobody should take my advice or assume I know what I am talking about. But it seems like everyone who owns Tesla that I know of plans to hold until they die. If the price goes up on tesla nobody would sell.
If this was another company joining the s and p where a large number of shareholders didn't have the belief that the company being added to the sp500 would become the worlds largest company and that the bump in price reflected an a higher than realistic price, people would sell and it would go down.
Personally - not advice - I don't see a reason to sell Tesla ever. Musk says he is using Tesla to fund his personal mars ambitions. I doubt he'll ever sell Tesla. Someday - maybe, 20 years from now, maybe 6 years from now - Tesla will be a rewarding stock to own. I'm just here to see what I should be excited about at this point. Why sell?
Um... How can he fund Mars mission using Tesla stock without selling?