We are in the process of establishing an accessibility testing green board for Drupal. A green board will allow us to know when accessibility regressions are introduced to Drupal core as we approach the beta and release candidate stages of the Drupal 8 release cycle.
The testing platform and tests are under development and progress is solid, thanks in major part to Kevin Miller (kevee). The tests register 257 failures currently (Nov 6, 2013), although some might be false positives and duplicates. We need developers, testers and reviewers to get us to robust test coverage and zero failed tests against Drupal 8 by 2014.