How much from the total amount of the Bitcoins mined so far are moving around within the Bitcoin economy, and how much are stored in wallets and never moving, and how much of those "never moving Bitcoins" are held by third party custodians.
It'll take a keener mind than mine to figure that out. It's tricky enough keeping track of the "lost" bitcoins where people assume access to the private key has been lost, but it's still largely guesswork, as it may just be long-term HODLing. I have coins that haven't moved in 5+ years, so do some people assume those coins are lost because they haven't moved in a while. But I would assume that because some early adopters have vast tranches of BTC and are more likely to be of the "hold your own keys" mindset, there should still be a sizeable sum in the hands of individuals.
Plus, it's pretty well established that these third party custodians are shit at security and seldom manage to retain custody of their clients' BTC, meaning it usually ends up back in the hands of individuals anyway.
But you understand my viewpoint, I hope. The "custodians" could cartelize, and could censor the transactions they don't want, or maybe censor some transactions labeled "illegal" by the government.
I don't think I did initially, but I'm there now. You're approaching it from the hypothetical scenario that a majority of Bitcoin users would be reliant on these companies and would then be restricted in their usage, correct?
From the perspective of someone who definitely wouldn't be reliant on those custodians, I'd feel a bit sorry for those "users" (technically, not really Bitcoin users), but that in and of itself wouldn't constitute a failure of Bitcoin (in my view anyway), as it's simply what those people opted to sign up for. No responsibility and no control. If that's what some people want, it's up to them. If, however, it begins to impact those of us who aren't using those services,
that I would perceive as a failure.
If, for example, such a cartel claimed they had an economic majority and somehow managed to pressure developers into going down a certain developmental path or otherwise interfered with network governance, that's where I'd draw the line. Provided the users who hold their own private keys are still free to transact in the way they want to, it's not a failure.