If PoS makes ETH a security, how exactly does the SEC plan to regulate it? Will they establish official policy that validators and full-nodes would be expected to follow, internationally or only nodes operated in the US?

Also, that's not how that works - consensus is entirely and originally international in governance. How can you declare the product of a wholly multinational distributed information network under the purview of your national bureaucracy by proclamation?

So, would it not be potentially listable on the NYSE as a regulated security in and of itself then? Seriously, what would this look like in practical terms??