Hope this thread is not too stale…
Making the whole of an ECM interface accessible and sexy is very difficult in the face of some of the 508/WAI requirements such as the ban on changing the display without notice and running without javascript. Alfresco's current use of AJAX presents a big obstacle to accessibility compliance at least for these reasons.
Some current Section 508/WCAG 1.0 requirements are admittedly outdated and are close to becoming obsolete with the release of WCAG 2.0, but it may take a little longer for these to filter through to the funding bodies like the EC and their contractual requirements. More contemporary requirements such as WAI-ARIA are a promising alternatives that may allow the sizzle and the access to coexist but they are even further out.
Even if the Alfresco 3.0 webscripts rewrite is nominally compliant it will surely remain a hugely complex interface that will contain untestable accessiblilty barriers that can only be identified by manual testing by experienced users of assistive tools. (This is only an issue if you want real accessibility as opposed to a tick in the box)
But its not all doom and gloom! The webscripts framework is your friend because it allows you to expose simple, truly accessible interfaces to a broad audience, while hiding the complexity of the administrative parts of the web client.
When accessibility is a requirement it will help to minimise its scope by asserting that the standard web client isn't part of the interface at all but just and admin tool. If you can convince the customer of that then you are free to provide accessible webscripts that are not only compliant to the letter of the guidelines, but actually inclusive of a diverse audience.