What would these be useful for?
If the sandboxing features a native containerization system relied on were also exposed via public APIs, those could could also potentially be leveraged by developer tools that want to have/use better sandboxing on macOS. Docker and BuildKit have native support for Windows containers, for instance. If they could also support macOS the same way, that would be cool for facilitating isolated macOS builds without full fat VMs. Tools like Dagger could then support more reproducible build pipelines on macOS hosts.
It could also potentially provide better experiences for tools like devcontainers on macOS as well, since sharing portions of your filesystem to a VM is usually trickier and slower than just sharing those files with a container that runs under your same kernel.
For many of these use cases, Nix serves very well, giving "just enough" isolation for development tasks, but not too much. (I use devenv for this at work and at home.) But Nix implementations themselves could also benefit from this! Nix internally uses a sandbox to help ensure reproducible builds, but the implementation on macOS is quirky and incomplete compared to the one on Linux. (For reasons I've since forgotten, I keep it turned off on macOS.)
One clever and cool thing Tart actually does that sort of relates to this discussion is that it uses the OCI format for distributing OS images!
(It's also worth noting that Tart is proprietary. Some users might prefer something that's either open-source, built-in, or both.)
UV is pretty good for python too.
Do you think people would be developing and/or distributing end user apps via macOS containers?
the firewall tools are too clunky (and imho unreliable).