The issue of accessibility in MediaWiki UX design has been raised numerous times in the recent past, most commonly in regard to font sizes and colors. I'm personally aware of it coming up at least 5 times in the past year (Typography Refresh, Flow, Echo, Mobile, NavPopups). Rather than rehashing the same discussions each time, I would encourage the design team to come up with a new set of accessibility guidelines that everyone can refer to and agree on. I would encourage stealing ideas from the en.wiki guidelines and the WCAG guidelines (
http://www.w3.org/TR/UNDERSTANDING-WCAG20/). I would also suggest that the design team invest in a pair of scratched-up coke-bottle glasses that each design mock-up can be tested with :)
Ryan Kaldari