Taking megaupload takedown into consideration this scenario is IMHO not only probable, but inevitable.
This is flawed comparison. I think we can assume that 90+% of Megaupload's traffic was illegal/cracked apps/games/movies/music. If 70-90% of all bitcoin transactions involved illegal drugs/weapons, then you might have an argument.
Bitcoin {IS NOT} a Megaupload.
Of course it is not. And we are not even talking about Bitcoin, but MtGox, specifically.
But how does that matter to the US government ?
They don't care what is and what isn't. They just call you a terrorist, send you to guantanamo and that is all.