MacOS apps can already be sandboxed. In fact it's a requirement to publish them to the Mac App Store. I agree it'd be nice to see this extended to userland binaries though.
You can't really sandbox development dependencies in any meaningful way. I want to throw everything and the kitchen sink into one container per project, not install a specific version of Python, Node, Perl or what have you globally/namespaced/whatever. Currently there's no good solution to that problem, save perhaps for a VM.
uv doesn't provide strong isolation; a package you install using uv can attempt to delete random files in your home folder when you import it, for example.
People use containers server side in Linux land mostly... Some desktop apps (flatpak is basically a container runtime) but the real draw is server code.
Do you think people would be developing and/or distributing end user apps via macOS containers?
