What I mean with "pragmatic cleanup" is getting rid of obsolete assumptions about the underlying hardware. E.g. two's complement has won, there's no reason why this couldn't be reflected in the C standard by removing signed overflow from the list of undefined behaviour. I bet more such cases can be found (e.g. 8-bit bytes, NULL not being zero, etc...).

Even if such exotic hardware is still around, the only thing that would change is that C compilers supporting this hardware couldn't call themselves "ISO Compliant" anymore, the users of those compilers wouldn't lose anything.