Do we support SRFI-6 string ports, reaffirmed by R6RS?
Do we support the with- and call-with- utilities?
"Reaffirmed" is a little misleading. SRFI 6 ports are created by OPEN-INPUT-STRING and OPEN-OUTPUT-STRING, and GET-OUTPUT-STRING extracts the text accumulated in an output port as a string. In R6RS, we have OPEN-STRING-INPUT-PORT and OPEN-STRING-OUTPUT-PORT, where the latter returns both the port and the anonymous extractor.
SRFI 6 is supported (according to the documentation) by PLT, Gauche, MIT, Gambit, Chicken, Bigloo, Scheme48/scsh, Guile, Kawa, SISC, STklos, RScheme, s7, SXM, Pocket, stk, and Sizzle, plus the R6RS implementations IronScheme, Ikarus, Larceny, and Mosh. Only SCM, SigScheme, and Scheme 9, plus the R6RS implementation Ypsilon, lack support for it.
Neither interface seems to me superior to the other, but I recommend we go with SRFI-6 because of its near-ubiquity.
The WG voted to accept SRFI-6 string ports as part of the core.