Thanks for the great link to a ongoing discussion!
And what a ongoing discussion it has been! Before we hear another round of why SilverStripe needs this. I like Sams post on the dev mailing list
Adding backslashes to URLSegments would be a lesson in pain.
And basically unless we find someone or a group willing to take it on Or a / few projects willing to finance to a extent the incredible amount of man hours involved this will likely stay firmly on the 'Nice to have..' list.