I'm in the process of building two websites using WP for serious companies.
If there is one feature I can think of that can really take WP to the next step in allowing us to use it like a proper CMS its the following:
Allow to set post order on category, including if the post has been assigned to multiple categories.
For exampls: I have a site about cars and wrote a post about a nice red Ferrari. So- I will apply that post to three categories: 'sport cars', 'Ferrari', 'red cars'.
Now I want the post to be in a different placement on each category.
If I can do that, I can use pages to navigate through static content and to get to categories, and use posts to have a proper dynamic CMS.
I've already seen discussions around the pagemash plugin and other places, the demand is high!