At Wikimania I found out that Marius Hoch ("hoo man") is contracting with Wikimedia Germany till September 30th and is specifically doing accessibility bugfixes. He says: "I'm always open for suggestions and reviewers/ testers for my changes."
So if you have a particular a11y pet peeve, or want to get his opinion on a change to https://www.mediawiki.org/wiki/Accessibility_guide_for_developers , now's a good time!