Well, after a bit of playing I have Simple Wiki Edit Mode running. It does what it advertises, ie. lets me edit my wiki's raw pages in Emacs.
It's a little disappointing compared to WikiMode for emacs. Navigating between pages is a bit clunkier. It currently doesn't handle free links, and #REDIRECTs require you to navigate directly. And I see a concptual flaw in what I want. When I want to edit pages with includes, I want to see the includes. But sometimes (when I want to extract the code) I want to see the result of the pages merged together. This would require SWEM to understand the two different modes (what in BEACH I call SourceView and PresentationView). To make this really work for me, you'd need some specialization so that the emacs client knew that it was working with a special kind of wiki. And ideally, when editing code, would know about the apropriate mode for the language.
But that doesn't detract from my previous point that Alex Schroeder is probably doing some of coolest and most important hacking going on at the moment. And a bit of work on this could produce something extraordinary. Note to self. Must find time to learn elisp!