The UK already aggressively shuts down bank accounts that have anything to do with bitcoin. I think we are counting down to when this happens in other countries too.
Is this true/why do you think(know?) this?
On topic: .gov isn't anywhere near as intelligent as you seem to think it is. I doubt anyone in a significantly powerful position even understands bitcoin (if they've heard of it) enough to know the 51% attack thing, what it means or how it works. Bitcoin would have to have a far greater number of users before "they" start paying attention. Great success is more dangerous than vulnerability.