There are many gaps in the current Form API:

• Its design dates back to a pre-OO era of PHP. We use Drupalisms like hash prefixes to distinguish different types of array keys.
• Widgets are not very extensible, and we've created widget systems for fields and configuration (admittedly with much code reuse) to make up for the gaps.
• The approach to altering creates difficulty for caching.

We could modernize Drupal's Form API, but it's probably better to move to Symfony's form component framework, as provides a promising OO-based, modernized alternative to what we've grown to love.

The presentation will involve an update to the discussion from d.o #1447712, including addressing concerns recently posted.

Useful preliminary viewing: http://drupal.org/files/symfony2-form-vs-drupal-form-api.pdf

I will also try to wrangle in a Symfony developer I know to help answer questions.