Emacs has been unexec'ing for as long as I can remember (which is longer than
I can remember Python :).  I know that it's been problematic and there have
been many efforts over the years to replace it, but I think it's been a fairly
successful technique in practice, at least on platforms that support it.

I've been using Emacs far longer than Python. I remember having to invoke temacs on something. Still, if I didn't know better, I could be convinced you were referring to the GIL. :-)