If you make a reasonable [and effective] effort to not conduct business with US citizens then they will leave you alone. The mere fact that I can access Deribit undermines their exemption.

But I've seen the SEC charge people with thinner rationale. For example, a eastern european guy in an alleged insider trading ring only traded CFDs on a European CFD exchange. The SEC claimed that he would know that the exchange would have to make corresponding trades and hedging trades in US equities and therefore he is culpable.

If it makes you feel any better, that particular case hasn't reached a verdict yet and was insider trading, so if you feel comfortable dealing with extradition hearings to establish case law in a foreign country or simply not insider trading on US equities, then you'll be fine.

The majority of the SEC's compliance statutes are levied on businesses that offer any product labelled a security. This is a well distinction defined and quite broad and very difficult to play wordgames with. Its just unfortunate that registration is so expensive.