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. 

Scoresby

bitcoin

How much bitcoin owned by ETFs is too much?

Good question, been thinking about this issue as well. But there are even more questions:
- How much bitcoin held by a single custodian is too much? (Looking at you Coinbase)
- How much bitcoin held by several custodians in a single country is too much?
- Can a single country gain control of the network by seizing coins and mining hardware from central entities?