Only 1 million people can hold 21 BTC.

In practice even less, because there's plenty of lost coins, and it takes quite a while before 21 million coins are mined, and most importantly, there will be a few super-rich who have far more then 21 bitcoin.       

So in practice, only a few 1000 people will have more than 20 bitcoin. Like maybe 100,000 persons or so.     

And yes, those will be extremely rich.     

I don't even think we will need to wait until 2035 for bitcoin to reach these kind of values either. But in 2035 it's pretty much a guarantee that bitcoin will be worth $100,000+ and probably a million or maybe even several millions.