I'd like to see a change in focus away from the Posts/Pages concept. I don't mean we stop using them altogether, but instead, change how we look at them in general.
Specifically go to a Pages/Widgets focus, and let posts, etc. be Widgets themselves.
I have a this visualized in my head well enough, but let me see if I can explain it clearly here.
Right now in the theme, you set up widgets for the theme itself and then the widget locations are theme based and they're across the board on all the Pages/Posts etc. However this is not practical and I've often had to use widget contexts to add/remove widgets based on the Pages I'm creating.
First, I'd recommend changing the Text Widget into a Widget that allows the same full text editing capabilities that the current main content of the page has.
Second, I'd like to see the widget layouts be able to be represented graphically in a WYSIWYG style format rather than how they are now.
Third, I'd recommend that the set up of the widgets in the Theme options be just a "template" for each page. Once you create a New Page, It pulls the widgets from the template and then you can add/remove widgets for that page. Part of this includes ditching the main content entry form and letting the improved Text Widget take its place.
What I envision this doing is allowing content to have multiple columns without a whole lot of tweaking with the themes and/or knowledge or how to set up floats on divs.
I'd like to be able to hand a WP install with a theme layout to a customer and let them control their pages without knowing very much html at all. We're very close to this now, but I think this will step us even closer.
Oh and one last thing, make the latest posts like what is used on the posts page be a widget as well, so that you can determine where and what page you want them to display on.
I know that most of this can be recreated using plugins, but I really would like to see WordPress lean towards this concept. Being able to design a page for any purpose, and the widgets are what primarily define the content on the page. This would be a major change from what WordPress is now, so I don't see it happening anytime soon, but it's an idea that's been rocking around in my head for a while. I figured I'd get it out before anyone got hurt.