As far as I can tell, POSIX was an attempt to codify existing practice amongst Unix vendors, picking the best of the most widely supported features, as opposed to actually trying to come up with a good standard. From reading UHH, one might almost be tempted to say that the only thing worse than POSIX was leaving things up to the vendors. Either way, POSIX seems to have dealt with a lot of interop issues, but it has fallen so far behind the curve that it hardly even makes sense to talk about. The article compares Android, OSX, and Ubuntu. If you were going to have a conversation about interoperability between those platforms, would you be thinking about POSIX? Or perhaps some web standard?

Standards probably shouldn't sit still, especially if they hew more closely towards existing practice than ideal practice. I think POSIX is overdue for an update.

As an aside though, did people ever voluntarily use csh? Aside from committed masochists, that is.