I've just put up a new and considerably improved tarball of the current status of Scheme48; since the last one, I've also moved hosts (and therefore email addresses & URLs), so it's now up at
http://mumble.net/~campbell/scheme/slime48.tar.gz
(and web-browsable in the slime48/ subdirectory of the same directory as slime48.tar.gz is in). Many features are still missing, but I've added important ones like evaluation in SLDB frames, an inspector, & I/O, and it's approaching actual usability now, I think, though there is a bit that would need more support on the Emacs side before I can continue and make it really usable in Scheme48 hacking. (For example, module control commands would be necessary for that -- commands which, for the most part, I believe, could be equally applicable to Common Lisp packages or ASDF systems.)
I think my question might have been lost in the traffic of the mailing list, so I'll ask once more: several people, including Marco Baringer, have suggested that it might be a good idea to add the Scheme48 back end to the main SLIME CVS source repository. I could fork SLIME to support the small changes needed for SLIME48 myself, but that would really be a pain to maintain, and I'd like SLIME48 to work pretty much out of the box. What do the SLIME developers/maintainers think about this?