The term millionaire is rooted in fiat. Should BTC replace fiat, 10 coins should be enough to classify as wealthy. That number can be argued. But we need a new term for someone with enough BTC that they are wealthy.
Is that a bitcoin millionaire? Anyone you know has a 1,000,000 BTC?
No, not to my knowledge no. No one ever owned 1 million, not even the super mega early investors and miners. But I could be wrong tho, no one can tell how many BTC a single entity owns by looking at the blockchain.