Because I was thinking about a specific case where I *could* configure how the subprocesses were invoked (launching a test server for a web application). It took Ned's comment to remind me of the original use case (i.e. coverage statistics for a subprocesses created by an arbitrary application, *not* a custom test harness).

What this would allow is the elimination of a whole class of ad hoc feature requests - any process global configuration setting with a Python API would automatically also receive a command line API (via -C) and an environment API (via PYTHONRUNFIRST).

Some existing options (like -Xfaulthandler) may never have been added if -C was available.

That's why I changed the issue title (and am now updating the specific suggestion).