This page is part of the web mail archives of SRFI 75 from before July 7th, 2015. The new archives for SRFI 75 contain all messages, not just those from before July 7th, 2015.
Let me quote Marc Feeley, one of the co-authors of this SRFI, speaking on this topic in another context:
"[I]f you can convince the RnRS authors to drop the ? on string=?, etc (but not on pair? etc) I'm 100% behind you [...]."
Also, I'd like to point out there is some precedent in Scheme for Unicode string comparison as currently defined in this SRFI, namely SRFI 13 (modulo question marks).