I would not consider this desire "misguided". Emacs is pretty old and creates its "own world", the problem so far was that most modern feature-rich editors are bloated (NetBeans, Eclipse). So people stick with emacs, vi, pico and their ancestors. However, Geany seems to have a quite reasonable plugin API (http://www.geany.org/manual/reference/howto.html
) though I have not tried it yet, and even though you can broach Greenspun's Tenth Rule, the fact that it bases on C makes it small and comparably platform-independent.
While I guess syntax highlightening and code folding should be quite easy, the question is whether it is possible to create something like a SLIME-plugin to Geany. As soon as that would be possible, it would be a nice alternative, I guess.
As far as I remember, SLIME and SWANK communicate using some RPC protocol, with S-Expressions sent from emacs to lisp. How hard would it be to partially implement it in C?