I like the Muun idea definitely, but I want to make sure that the solution survives them losing or breaking their phones, so that's where hardware wallet may be a good solution. But I'm still missing multiple things there, like good guidance for what to do with it, how to monitor the price, where and how to hide it and back it up, etc.

We can definitely do a steel backup, have lathe available and have 3D printer available too. So I'm thinking that would be part of the story.