I'd love to see a calculation (although I'm admittedly far too lazy and technically incompetent to do it) to add up the number of bitcoin held by exchanges in their own treasuries, plus in customer accounts at exchanges, plus BTC in non-exchange wallets, dormant wallets/lost keys, ETF's etc.
Then see if that balances with the number that have been mined so far. Just to make sure there aren't any which are being double-counted somewhere along the line (for example, exchanges nominally holding them in customer accounts, but maybe not buying in enough BTC to cover it - a kind of crypto fractional reserve banking).
That's a good point. Blockchain is transparent and I guess that some sort of such calculation has already been made.
I can try to look for it. If I will find something, you will see a post about it ;)