For sure billionaires invest in btc. Why wouldn't they? They probably invest in a lot worse things. I imagine most billionaires, even though they have billions, would have noticed the amazing rise of bitcoins by now. These kinds of people have an eye for that sort of thing. Billionaires didn't become billionaires because they waited for the mainstream media tell them what to do like most of the sheeple do.
I think you're right. If billionaires are still looking for investment opportunities they would've certainly heard about bitcoin. Some might see the tremendous potential it has. Some won't.