I really don't think much of the billionaire's will be investing into bitcoin. Because they probably have already been making a good amount of profit through real time business. But more and more has started to invest into bitcoin related business as they have started to understand the real value. But billionaires, there were just a few that i heard of.
Maybe we only heard a few, or maybe they don't want the public to know that they are also investing in bitcoin in their portfolio. But for me, I still think that billionaires has been investing in bitcoin as well. Because just like us, we find bitcoin as safe haven for storing our wealth. We just don't really heard from them much because of concern like security or someone will try to hack their wallets.