> ...it's unmatched for batch uses...

Quite possibly. I know that it's what Openstack uses for virtualization.

> ...to interactively step into...

Sure, running on an emulated CPU can be very nice.

> ...like as something part of a distro build chain to allow non-cross-compilable packages to be built for ARM on x86-64...

This sounds like it would be incredibly slow. As in "It's better to just buy some inexpensive ARM PCs" slow. I know that GCC and Clang can cross-compile just fine. It looks like Rust cross-compiles, and I think Go does as well. Do you know of major tools and/or languages that don't cross-compile?