I seem to be misunderstanding you, then, and for that I apologise :). I think there is a risk of breakage (I'm not a technical person, but doing pretty much *anything* creates some risk of breakage) but I disagree that we're not going to get the expected results.

There are two problems with getting users to participate with Wikipedia (well, 3, but we won't get into "most people don't know they can edit"). The first that concerns us is the technical hurdles; the fact that markup is complex and most people don't understand it. The second is the social hurdles; the community is not, quite a bit of the time, a fun place to be - nor is it something that can be understood easily (we have policies out the wazoo, mostly in technical and internal terms). To "fix" Wikipedia's participation issues, we need to fix both problems.

The technical hurdles are at least partly fixed by the visual editor. This is a necessary component if we want to improve things - it's not, however, the only component. Even with the visual editor, getting people to stick around is going to be difficult because of the social issues (although the New Editor Engagement Project is working on ways to solve those, too). We might get more people, but that's only because we're exposing more people to the possibilities of editing: I doubt the ratio of success:failure in terms of long-term participation will dramatically alter. That's where the second element comes in; fixing social problems. Hopefully those efforts will succeed, and the result is we'll have an interface that's open to newbies, and a community that is as well. All this is going to take a long hard slog though.

Crucially, however, just as the technical improvements won't work without social improvements, the social improvements won't work without technical ones. We're not going to see a massive boost in numbers from exposing lots and lots of people to a culture marked "here be dragons", but similarly we're not going to see a massive boost in numbers if we don't expose them at all. We need to fix both the technical hurdles and the social ones - and that's precisely what we're doing. I don't think anyone is claiming that the visual editor will, in and of itself, be the solution to our woes. But it is an essential component of that solution.