Genesis Accessible is a plugin for site owners who want accessibility-ready websites, but who use themes which don’t yet support the Genesis Framework’s accessibility features.
Do you need the Genesis Accessible plugin? Maybe not. Version 2.2 of the Genesis Framework was released in September 2015. Since then, most child themes have included support for Genesis’ built in accessibility features. If your site is running Genesis 2.2 or higher (Genesis’ current version is 2.6.1), and you have a child theme active which includes accessibility support, then you already have most of the features offered by the Genesis Accessible plugin.
Not sure if your child theme includes accessibility support? You can visit the StudioPress themes page, select “Accessibility Ready” from the “All Features” dropdown, and see if your theme is listed.