I'm actually really curious, how could the SEC (or any agency) take any action here? Sure, they can make rules that say you shouldn't trade bitcoins, or maybe even threaten fines ... but for someone who doesn't care to report their activity, is there any way to be "Stopped" from doing so?
By no means am I a securities or legal expert but the SEC has authority to regulate any marketplace, exchange, or "investment opportunity" to ensure investors are protected from fraud.
Does it really matter which US-based regulatory body I'm dismissing as irrelevant? The long-term impact of Bitcoin is way bigger than any one country or culture.