I think you can learn the skills within our existing legal framework. If I were to introduce someone to firearms that has no prior firearms experience we'd be starting with a 22 or maybe even a pellet gun. Access to currently prohibited weapons to further advance individuals that already possess skills is a completely different topic. This doesn't even start to address the realities of the role of firearms in modern conflict.
There's lots of more valuable ways for people to spend their time "preparing" for whatever the future holds for us. If someone thinks that prohibited weapons are the key to survival they can seek training through other means like joining the reserves. Or take an active role in politics and work towards changing the legislation. Or if things are so bad already then break the law and learn/possess those weapons anyway.