I'm occasionally (when I find the time) putting some work into blending the forum and wiki skins so they merge seamlessly (it looks ace but still has a few issues that need fixing at the moment). So to include the visual editor I'm sure would add extra time and effort to this work - but without starting it, it is hard to know how much.
Really depends on whether we see any benefit from a visual editor - does that make it more accessible than, say, someone producing the text, and someone else more familiar with wiki formatting tidying it up - which seems to be how we've done a few pages.