Of course, you try to overthrow the government in its current state, you'll be branded as as terrorist instantly, and shipped off to Gitmo... so the 2nd Amendment is outdated simply by the fact that the US Government's militia is easily powerful enough to suppress the US populace, even with defections.
It's not even an issue of force majuere...
Cut off FOX and Schlitz long enough, and people will be howling to have the current Govt remain in power
Sadly, it's probably the same down under.
Sure, our army would have difficulty holding a city, but our population is so lazy, the closest we could come to armed resistance of the Govt is outsourcing for some Indian and Pakistani radicals.