Someone made an important point to me in a private message, which is that even if the regulated exchanges don't have to confiscate or freeze the tokens subjected to a regulation action, then even just delisting would be enough to cause liquidity and prices to crash.
So all investors globally are affected, not just USA investors.
There are no unregulated exchanges of any significant volume. And appears there won't ever be.
ICOs quack like investment securities. The USA Supreme Court ruled under the Howey test (numerous times) that obfuscations of the economic reality of the situation are not a valid excuse.
But that legal position seems to meet (i.e. be regulated by) the Howey test in the case where the ICO investors are clearly buying tokens with the expectations that the developers are going to deliver certain actions with certain timelines as reinforced by the concept of escrow agents, published timelines, and perhaps even an oversight foundation
...
In short, if there is centralized control of the flow of money from investors to the activities that token investors base their investment expectations on, then the Howey test seems to be met.