I thought about how I would go about 6102 if I was the government. I think I could easily attack KYC Bitcoin that was taken into self custody. From the exchanges, I know who bought Bitcoin, how much and for what price.  So I declare self custody bitcoin illegal as of Dec 31. I call that a taxable event and would be able to compute how much tax you now owe. I might even set a flat 50% tax regardless of income bracket. I flag your accounts for automatic audit and if I do not receive the expected tax by April 15, I send the IRS after you with threats of jail time. Most normies would need to sell their bitcoin in order to pay the tax. 

It also depend on why I am after your Bitcoin. If it is self custody is a threat to the dollar and my monopoly on money printing, then I would not go after the ETFs as that Bitcoin is locked up as an asset and cannot be used as currency. I may even allow self custody owners to trade their Bitcoin for equivalent ETF shares tax deferred, similar to the 1030 exchange in real estate. 

I guess I don’t see a scenario where the government confiscates Bitcoin held in the ETFs and exchanges but does not have a plan to confiscate self custody bitcoin that was originally purchased from KYC exchanges. The taxation, IRS scrutiny and jail time threat eliminates any “I lost my Bitcoin” excuse. For this initial attack, I don’t care how you get the money because I know most people will only be able to get it thru selling their Bitcoin. If you truly lost your Bitcoin then that’s terrible news for you. Because I’ll garnish your wages or put you in jail or both.