I may have spoken too soon when I said that I was still interested in hosting SLIME48 in the official SLIME repository, since it seems that there may be interest all around in forking SLIME for SLIME48. I'd therefore like to poll this list's subscribers to see who would prefer this option, which I'm now ambivalent about. In order not to clutter the list, though, please send responses privately via mail, or contact me on IRC (in #lisp or #scheme as Riastradh on irc.freenode.net).
To clarify briefly: by a fork of SLIME for SLIME48, I don't mean to make a fork that is completely oriented toward Scheme48 (or Scheme48 & MIT Scheme, or whatever), but rather to make a more clearly specified network protocol for communicating between a user interface and a Lisp system, less particular to Common Lisp or Emacs than the current Swank protocol is, and to hack the existing SLIME & Swank code to implement this protocol (which would not be very different from Swank).