Several persons attending the recent WikiConfIndia 2011 drew attention to the need for greater ease of use for persons with visual challenges - Barry Newstead referred specifically to this need, commenting that in general, usability improvements for persons with special needs pay off for the community at large.
This recent development at Stanford http://www.springwise.com/lifestyle_leisure/braille-writing-software-touchsc... how visually impaired persons with Braille skills can interact directly with touchscreen devices. What is very striking about this solution is that it does not involve tactile feedback, as one might expect. Instead, once switched to Braille mode, the screen senses multiple finger placement and translates that into the expected Braille codes (see the video to understand this, if you are unfamiliar with Braille typing).
To echo Barry's comments made at WCI2011, I think a certain amount of such out-of-the-box thinking could go a long way to creating an interface that is intuitively more approachable than the present wiki editor.