As far as I know, Grayscale is by far the biggest player in the BTC ecosystem. As per the attached spreadsheet they now control more than 2% of the entire BCT supply. Square is getting bigger, and
other competitors just started taking steps in this direction, given the huge amount of money to be made. Yet, the pressure is not against the newly mined bitcoin, but against the total supply. So a lot has to be done. But nonetheless, I expect this business growing steadily over the next quarters. Remember that bitcoin is still tiny. The entire market cap of Bitcoin is equal to the market cap that Amazon raised in the month of July only(more or less 220 billions).
Coinbase holds around 1 million coins, that's 4.7% of Bitcoin's supply. And technically, Satoshi also owns 1 million coins, so he's also the biggest player in Bitcoin ecosystem, though he's disqualified cause he's inactive now.
Still, holding 2% of supply is pretty big. I wonder if there's any entity that holds 2% of all gold in the world?