I feel compelled to remark that they wouldn't do this just so they could flip the switch and screw over some people holding bitcoin. The NSA has easier ways of screwing people over.

Instead, as PG and others have hypothesized, the sovereign behind btc will have achieved a new worldwide currency system, that naturally, they will participate in, perhaps from a somewhat advantageous position (premined blocks etc).

The last 3 sentences of your post are a non-sequitur imho.