Working code at https://github.com/sillygwailo/Readability-Button with an official Drupal project at http://drupal.org/project/readability_button currently "only" adds Readability buttons to nodes and adds a quick way to verify the domain without having to modify the theme. Both features are available for both Drupal 6 and Drupal 7.
This is not a page for ideas about Readability the service. There's already a place for that at http://readability.bonfireapp.com/
Ideas for further features:
Override individual nodes
if the content type is set to display the button, the override for the individual node would not display the button
if the content type is set to not display the button, the override for the individual node would be to display the button
since the button requires an ID block, the button can only be shown once, so the module should decide which gets the override
implement the Readability publisher's API:
may want to first implement the API in PHP, then use the library to implement it in Drupal
would probably require the Drupal OAuth module for authentication, not yet ported to Drupal 7
which features to implement?
maybe it assumes a model where a user matches up their Readability account with their Drupal account, and from the Drupal site, they can interact (at least in the back-end), with Readability. For example, if the Drupal site is a news site, they could allow Readability access to their data, and if that user makes an action, it gets sent to Readability for archiving and/or credited as a contribution