I think they have already seen the potential of bitcoin. Some of them have already invested, but they will not show it. They are just gaining more money by investing in bitcoin.
They can just invest, because the money they give for a investment is nothing for them actually.
We can not say how much they can invest or are investing, it could be really big number. We all know that if you invest more, you will gain more. So I guess that you are right when you say that there are billionaires in Bitcoin world. I mean why would not they be part of it, they want to make more money, and Bitcoin is easy way for just that. And of course they will not say that they are into Bitcoin, any smart person stay silent when they are making big money.