In my opinion, the decision to cross your arms and pretend there is no issue is unprofessional.

Summary of your arguments:
- It's Microsoft's fault.
- Windows accepts backslashes anyway.
- Shell detection is difficult.
- It's a complex issue.

None of this is relevant to addressing the issue ThurnerRupert was facing. He asked to be able to CONFIGURE the path seperator. This needs not involve shell detection (which is indeed brittle). This could be handled simply by the user setting 'os.sep' and having os.path.join() and friends use that.

I'm using SCons on MinGW and the build is failing due to the messed-up paths.

<rant>
I'm less than thrilled about learning that this won't get fixed. I feel that one of the important strength of Python is that it "just works" on many platforms and this amply justifies this issue not being treated with such frivolity.
</rant>