If the Berkshire news is actually real, it will definitely cause a rally in the share price. Anytime Berkshire reveals a stake in a company, that stock rallies just off of that news alone
Berkshire Hathaway, first bought 10M shares of Apple in May 2016 for $232M.
As of September 30th, 2020, BH held 965M shares of Apple currently worth $131B.
So
if BH shows they initiated their purchase of Tesla, it will not be a one time event. BH are long term investors and will likely continue to purchase shares going forward at higher costs (similar to their AAPL position which has growth 10X in quantity of shares owned since their original purchase).
We will find out by February 16th if BH now holds Tesla. If not, it is only a matter of time before they do. BH was many years late on Apple. Apple released their orginal iPhone June 2007 and BH waited nine years to get on board. Still BH have done very nicely with Apple, as they will do so with Tesla. It's just a matter of time.