I have been writing up a white paper on how Drupal could work, but wanted to submit an initial and important first step. I know allot of people see comments as nodes being a major issue. Many want it, while others site potential problems with performance. Without comments as Nodes we have no code uniformity making any CCK features and Views features needing exceptions based on if its a node or if its a comment.
What if I could tell you that I could make comments as nodes and not effect performance? What if I could tell you that on very large sites (like Drupal) I could actually enhance performance across the site? The solution is simple. What if we gave every content type its own table? The current "comment" system would simply be a content type that uses the new unified content structure. Since the default comments content type would be "comments" it would have its own table, as would stories, pages, books, etc.
The second step of this (but not absolutely needed) is to include views into core, and be able to attach views to content types. An example of a Content Type "Article" would be a content type with a Title, Body, and lastly a "comments" view. In addition we would have a content type called "comment" (notice the singularity).