It's true that this statistic is global, and sounds more dramatic than the reality probably is. But if the trend continues, it is not unreasonable to expect a custodian like Coinbase to end up with several million btc.

I had the coinbase situation in the back of my mind when I wrote the poll. Clearly, if a single custodian had a very large percentage of the total supply, it would make things like forks much more difficult.

I also imagine if one entity controlled something like 20% or more of the supply and had a chain analysis business, it would make on chain privacy significantly more difficult.