Feels to me like raw strings has evolved so I’ve prepared an implementation and made a toolchain available (it appears as a dev snapshot for the 27th and you’ll need to restart Xcode). The toolchain supports both # and ` (backtick) as a custom delimiter and a “differentiator" prefix of #raw or raw if you want to help test the implementation.
I found the visual weight of # to be a virtue in a delimiter when compared to ` but #raw as a prefix to be asymmetric and one # too many when compared to just raw.
I suggest we should make a start on writing a proposal for review with the syntax:
raw”a raw string”
raw#”a raw string”#
raw”””
a raw string
“”"
raw#”””
a raw string
“”"#