I don't think it would simplify things that much. Having multiple users at the OS level is useful even when there's only one human user. For example, you can r

I don't think it would simplify things that much. Having multiple users at the OS level is useful even when there's only one human user. For example, you can run a service as a user with limited privileges, to contain the effects of a vulnerability or breach. Anyhow, sandboxing is just as necessary on a single-user OS as on a multi-user OS. And it's much more complex than multi-user support.