In reply to Justin Tadlock.

People aren't demanding accessibility-ready themes because they are not aware of the importance of accessibility. The onus is on us - the people who build the web - to educate the people who use it on the need for accessibility, and to provide fully accessible solutions.

As for making accessibility a requirement being the wrong approach, you should have a chat with the EU. Or the US government. Or the Canadian government. Or any of the other governments around the world who are now legislating accessibility as a core requirement for websites. That's the incentive: Without accessibility in themes, WordPress will rapidly become problematic for the end-user.