I think there are a number of ways that Drupal 7 could be much more accessible out of the box than it is right now. I've spent a bit of time working on a few items to improve and document some accessibility enhancements. Spent some time going through WCAG 2.0 documentation & comparing it with Drupal Core. And have been making patches and proposing best practices enhancements for a number of projects.

I'm definitely much more of a PHP/MySQL developer, but the complexity of finding a neat solution that works for SEO, across all major browsers, and also with several screen readers is pretty intense.  Since more and more websites are needing to comply with accessibility regulations this is going to be a larger problem for all of us.  Having a few good best practices outlined and tested in Drupal core will help all of us just implement more accessible websites by default.

The technology is changing quickly, but the guidelines for accessible implementations are as well.  Particularly with the more interactive components that have been included into Drupal core, the awareness of ARIA standards will be important.  There is a growing community of people participating in the Drupal Groups keen on accessibility issues, but with a mix of experience & expertise. 

Building consensus takes time, however, getting a critical mass of people to review patches and demonstrate that they are useful and don't interrupt other functionality isn't easy. Different experts point to different solutions and none of them seem to be looking at specific applications platforms like Drupal.  With all of the money that people have invested in generic accessibility initiatives, one would think it would be fairly easy to get support for improving a specific and popular open source implementation that will improve accessibility for everyone (even if an individual developer isn't at all knowledgable about accessibility issues).

I was encouraged though when driving down to DrupalCon in Washington, DC that this is an issue that is being taken more seriously, even at the gas pump.  Hopefully we'll be able to get a bit more agreement around these issues in the few days we have at this large conference. 

ps. This is also a test to see if this post shows up in Drupal Planet. We're happy to be listed here!