All of that is technically possible under Linux. I think the biggest issue with Linux for macOS enthusiasts is that there are very few macOS enthusiasts who are

All of that is technically possible under Linux. I think the biggest issue with Linux for macOS enthusiasts is that there are very few macOS enthusiasts who are willing to write their own window manager/composer/GUI toolkit/distro. The keyboard shortcuts can largely be fixed, but many of the advanced ones are modeled after Windows rather than macOS when it comes to behaviour. The window bars will require a new (or old, as in Mir era Ubuntu) paradigm, which will require convincing application developers to use it, or for a distro to make their own alternatives. The disk images thing sounds quite feasible using standard qcow2 images, though you'd need a file manager with support for them. I think macOS enthusiasts are generally quite happy with macOS, so I don't really expect a real macOS based Linux environment any time soon. This stuff requires more than just theming, the entire standard application stack would need to be rewritten, as well as parts of the input stack.