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.
It is a fiat term to own 1million of any fiat currency but being one in one does not mean you are in another does it. I think 10coins just means you are testing the waters not that you are wealthy by any stretch of the imagination.
The term for someone who has a very large stack of Bitcoins is whale and i like that name for the wealthy who hold a lot it make sense the one thing we need to work out is how much Bitcoin someone needs to be a whale? 1000-10,000-100,000