In reply to Jeff Chandler.

I don't know about impossible, but certainly very, very difficult. And that's not the point of the WordPress accessibility-ready requirements; these are targeted at a very basic level of accessibility, to ensure that certain fundamentals aren't ignored. Ultimately, in every case, the accessibility of the site is the responsibility of the site owner - but if we can provide themes that don't require thousands of dollars in modifications just to meet basic requirements, we'll make that much less painful.