I don't see this as much of a downside, because calling attention to the different parsing rules seems like it might even be a good thing. I like # as a delimiter modifier, and would rather just have one simple form than open it up to arbitrary ones. I don't see the need to support #raw(”a “#raw” string”) and similar from @johnno1962's examples.
One question that is still open in my mind is if this should be supported for regular string literals. Is this desirable (and implementable):
let s = #"non-raw string with "quotation marks" that don't need to be escaped"#
If this is not desirable then why do we need a r/raw/#raw signifier at all, i.e. why isn't the above the syntax for a raw string, always requiring at least one #? Perhaps it isn't clear enough that the string is raw, or perhaps isn't implementable (ambiguity or other parsing difficulties?), or perhaps someone thinks there will be a need for further types of string in future so they want a syntax that generalises well. Does anyone have any opinions about this? Will further types of strings be required, like the “raw string with interpolation” that @johnno1962 mentions? My feeling is “hopefully not”.
I would also appreciate it if someone would weigh in on the difficulty of implementation here, and perhaps how well this will be tolerated by external tools like text editors. What is your experience there for Rust raw strings, @Lily_Ballard?