I think at a general level, your criticisms are a good attack on
a style of I/O programming.  However, it isn't a style of I/O
programming that is going to go away, and I think it is worth
supporting, cf. Bear's last message for a defence that C-style
output, if broken is at least not abjectly broken.

Maybe a useful way to advance the discussion is to break it up
in two parts:
   1. Merits of C-style vs. functional-style output formatters
   2. Merits of Ken's proposal as a C-style output formatter

Maybe also it is worth the final SRFI including a relationship of
the C-style formatter to a functional style formatter (eg. the
semantics could be a transformation from the one to the other).

Specific points and criticisms:
  1. I think single letter escapes are fine: like mathematical
  constants if you use or often read them, you'll remember them.
  However, I would like it to be the case that you don't need to have
  memorised the whole table to be able to tell consuming escapes from
  non-consuming escapes (eg. upper case vs. lower case, alphnumeric vs.
  other).
  2. Is it good to have both ~? and ~K: why have backward compatibility
  cruft in the first SRFI?  Explanation, please!
  3. It seems to me the nicest functional formatter uses the standard
  string concatenater together with quasiquotation.

Charles