Aaron Jorbin writes about his goals for the Twenty Thirteen default WordPress theme. He envisions an accessibility first approach, saying:

Accessibility First would involve a few decisions to be made upfront:

  • Color choices with high contrast in mind from the start. This is one area that Twenty Twelve barely missed.
  • Color choices with multiple types of color deficiencies in mind since an estimated 10% of all males suffer from some form of color deficiency.
  • Making up for browser deficiencies, specifically the skipnav focus bug in webkit
  • Make sure that the design still looks beautiful when the font size is increased 200%
  • Following the Theme Accessibility Audit Draft Proposal

I love this approach, and taking Twenty Thirteen down this path would bring accessibility to the forefront not just in the WordPress community, but the web in general.