USG basically tried once to mandate backdooring encryption itself - in the 90s, when the entire topic was only relevant to a small community, there was basically no low level "street crime" involving encryption, and doing so required restricting individuals' distribution of software.
The renewed push is based on telling commercial companies that they have to setup their systems to assist the police, completely in line with precedents like CALEA. The much more diffuse tech-using community is already primed for heavy handed authoritarianism based on how these companies already operate, and also in general due to being pumped full of the terrorism by the 24/7 "news" cycle. I'd hope you're right that the US has constitutional protections to backstop this, but from my perspective those "protections" serve more as coping mechanisms rather than as effective restraints on government power.
I can perhaps see a legal exception for US Free software devs who aren't working commercially, but I can just as well see a malinterpretation declaring them as engaging in commercial activity ala Wickard v. Filburn.
Each nation in question has different protections, or lack thereof, when it comes to privacy, speech, property rights, et al. One size will not fit all, each country would see a different response to the same attempted legislation. The US Government has tried for two decades - with very little success - to reach for something equivalent to what Australia just rushed through in no time at all. What would completely rewrite so much US law and interpretation so rapidly as to make such a drastic change possible in the US anytime soon? Nuclear terrorism, as a society shaking event, is about the only thing that comes to mind as plausible and that's far-fetched.