Hi. Interesting. Have you tried the "Custom Write Panel" plugin? It looks nice and basically functional (although a bit finicky with WP 2.3.3) but I wonder if that's the best way forward as a major in-built code change would screw up all the data that I enter now using this plugin.
I am amazed that this basic feature of any modern blogging or CMS platform is not built into WP with a little more sophistication that silly key-value pairs. The entire "Write" panel should be customizable, ideally even by category. E.g., my same blog could have a News, a Book Review, Movie Review categories, for which different info is required and the admin interface should allow me to reflect this is in the labels and input fields, instead of putting stuff in generic "Excerpt" or "Body" areas.
EE and MT both allow this seamlessly now.