Maybe, but wouldn’t the customer have to know how to run QEMU? I am imagining a customer who wants to just replace an old machine while changing as little as possible.

Since this install is based on QEMU running in Linux, it would not meet that need.

The end user need not know it is QEMU atop Linux. They see and use DOS.

Yes, but inside a VM. What access to real hardware (e.g. to communicate with the outside world) does the user get?

Whatever is configured with QEMU: everything if that was the use case.

But it looks like their setup is not configured to give access to hardware, at least I didn't see any options on the command line.

Highly unlikely, without really messing around with it.