I recently tried to measure coverage of a program that calls os.execvpe, essentially causing the process to be replaced by a different one. This did not record any coverage information at all.
The reason of course is that os.execvpe does not return, so there is no opportunity to call coverage.stop() and coverage.save() as is done if e.g. an exception is thrown. I'd suggest this method could be "monkey-patched" so that such code can be inserted before it. (and also the other 7 os.exec* methods of course)