Unless you are especially enthusiastic, I'd rather have you work on any or all of LogisticRiastradh (mostly just pulling together code from MIT Scheme using the links there), NumberStringUnicode (trivial, just number->string, string->number, and digit-value), and/or NanMedernach (easy on top of (rnrs bytevectors); there is a portable implementation in the SRFI 4 config directory called (r6rs bytevectors)).  There's no pre-SRFI for LogisticRiastradh, just a list of what procedures must, should, and may be exported depending on what you think makes sense.