Drupal 7's theme layer is powerful, flexible and massively complicated. With the introduction of the Render API into our template files and the double preprocess/process functions, the number of different ways that a piece of content might get rendered has made it difficult for themers to figure out... what the hell is going on at any given moment. A glimpse of some of the problems Themers face with the new D7 complexities can be seen in the "Separate usage of hide(), render(), and other template features from print statements to enable non-developers to create themes" (originally "Remove data structures from templates") issue on drupal.org. But it's time to focus those raw frustrations and do something. Instead of letting the theme system organically change (piecemeal), like D7 changed from D6, let's plan the next generation of the theme system by:
Documenting problem areas (insolvable bugs, mis-features, inconsistencies, etc.)
Documenting features and abilities we'd like to keep
Figuring out new and better features we'd like to see in our theme system
Item #1 is already being compiled on drupal.org in the "Gather pain points from themers about the theme and render system and develop an action plan to address them" issue. You can help out tremendously by posting your thoughts over there now! The presenters will compile that list and work with other Drupal developers (like Moshe, Sun, Crell and Jacine) to create suggestions for #2 and #3. (If you'd like to help with #2 or #3 before Drupalcon, contact JohnAlbin and we'll cc you on the email discussion.) This will be a collaborative discussion and planning session. It will likely require a follow-up BOF. The goal will be to come to consensus on how we want the theme system to actually work, so that we can start building it.