China is the main source of Bitcoin mining, and uses this to generate currency through market manipulation. Large scale national players can cause huge volatility and then capitalize on the dips they created.
Any number you can think of, I can double.
First we had fiat money, virtual money is worth even less without real assets. Blockchain is a great technology for a lot of transactions, just not as real currency.
I think that AI will eventually break blockchain. Hold something real.