Up-to-date standards are offered for checking compliance, and it provides a cost-effective way to scan a site for compliance. There's services out there where it'd cost more than $150 (the current cost of a 1 site 1 year license) for the size of the sites I'm working with. I'm very happy to see this offering in the first place, and it's even nicer to see how thorough it looks to be. Of course, it's not perfect so I'd love to see more of the WP.org listing fleshed out (the developer author/contributor mention is missing, etc.), I'd love to see the free version on GitHub (or similar for community development assistance [I have a few things I'd help with] which is very nice to see in a WP.org listing to show there's support / ongoing development for the plugin), and of course I'd love to see the server-side checker come to feature-parity with WAVE (currently WAVE is showing a few things the server-side checker doesn't have [color contrast, etc.]) Keep up the great work!
WordPress themes designed with accessibility in mind tend to be easier to use and clearer to navigate than their contemporaries. While you may have specific goals in mind like ADA compliance or WCAG 2.0 standards to pass, rest assured that you won’t have to sacrifice on design quality. You’ll likely find a theme with a higher standard of design by searching for templates with these requirements.
On the legal side, ambiguity in the law and the speed at which technology and dependence on the Internet has developed created an opportunity for litigation all over our nation. As these cases have moved through our system, the courts have been nearly split -- with the 1st, 3rd and 7th Circuits ruling that the ADA does apply to websites, while the 6th, 9th and 11th Circuits have ruled that it does not. These latter rulings have all been based on the interpretation that the ADA is focused on physical location and requires a nexus test. Other circuit courts in the United States have yet to rule on the topic.