Thank you for the comments.

 > 1. Gauche has been using #"..." syntax for another purpose
extensively.  It's nonstandard after all, so no other implementations
are using it, we may add a reader switch or something to support
srfi-267.  If the conflict can be avoided, it's nice.
 >
 > 2. The delim within "" does not obey string syntax, yet it does look
like a string as it is surrounded by double quotes.  Although the rule
is clear, it may be a source of confusion at a first glance.

There isn't a good ASCII replacement for ", as ` and ' are already taken
by syntax-case. Other proposed syntax was very confusing (using escape
sequences to denote raw strings). I'll note the conflict in the next draft.

The delimiter should be thought of as directional quote marks, like
#“delimiter“raw-text”delimiter“ (or using guilements,
#«delimiter«raw-text»delimiter»). Syntax highlighting should be able to
make clear the delimiter portion of a raw string.

An alternative might be #"delim(text)delim" like in C++, but specifying
and implementing that was slightly trickier and treats brackets in a way
that is different from all other uses of brackets.

-- Peter McGoron