So you think creating an imageboard only in Flash would work any better? Flash, as well as HTML and CSS, is about structure and styling of information.
It goes without saying that any system relying on user interactivity requires a backend.
Speed is certainly of great importance. That, and minimizing overhead. I would also love to use this project to demonstrate that Flash doesn't /have/ to be a slow and cumbersome affair, and that if done right can actually enhance an experience.