From your title my immediate thought was "cool, maybe this will move us a bit closer to making components (or the testing thereof) cover accessibility thoroughl

From your title my immediate thought was "cool, maybe this will move us a bit closer to making components (or the testing thereof) cover accessibility thoroughly by default". See, the idea with the semantic web, and the ARIA markup equivalents, is that things should have names, roles, values, and states. Devs frequently mess up role/keyboard interaction agreement (example: role=menu means a list will drop on Enter keypress, and arrow keys will change the active element), and with ensuring that state info (aria-expanded, aria-invalid, etc.) is updated when it should be. Then I checked the Antithesis website. They don't even have focus state styling on any of the interactive elements. sigh