Earlier quoted context omitted.
It might not change the overall ecosystem that much. Many companies doing ICOs are already locating themselves in friendlier jurisdictions, and making some effort to block U.S. contributors.
What efforts are these? All I've seen are checkboxes on their web site making the user tick a box confirming that they aren't a US citizen. Geo-blocking US IP addresses won't work either, because an ethereum contract can't refuse a transaction based upon its source IP address (it doesn't know it). So if an ICO publishes their ethereum contract address online (e.g. via a twitter post), they are implicitly advertising…
To my way of thinking, if you're sophisticated enough to do that, you're sophisticated enough in blockchain matters to make your own investment decisions.