Form error UX feedback wanted

I'd like feedback on a proposal for how Form Errors work in Drupal 8 core:

http://groups.drupal.org/node/209513

I've created that Wiki page with proposed screenshots in response to the lengthy discussion in issue #447816 about how Drupal core FAPI indicates form validation errors using color.

In brief, the proposal is that error messages be made available to users in place at the location of the field that has the error. A summary of errors would still appear at the top of the page. Here is a taste of what you'll find on the wiki page:

Please review the full proposal here:
http://groups.drupal.org/node/209513