People don't know how to type them on a US keyboard, so it'll never pass the "if I can't hand-write this in ed(1), it isn't a valid file format" hacker adoption barrier without someone of Google's size to force us all to adopt it (e.g. protobuf).
I believe you could type it in DOS with the same trick that works today: Alt-028, though nowadays you have to say Alt-001E due to Unicode. (Actual ascii/uni codes may vary.)
Perl6 tried incorporating non-US-keyboard characters into the language and that went very badly. I'm sure it works fine for Perl6 people, but beyond that boundary, I still encounter people who can't type é on a Mac with the keyboard alone today, much less handle Alt-001E. So I am extremely pessimistic.
