I wasn't aware of this being a problem in practice, do you have a reference for that?
That doesn't capture my uses of these functions. Maybe those are a bit niche, since cargo-miri is essentially doing nothing but setting up the environment for invoking cargo. It's more like a giant shell script. And in a shell I can mutate the environment easily and safely (well, "safely", it's still a shell script).
I'm also absolutely in favor of having those APIs. I am just not sure it's enough.