I started a discussion on Area51 about the UI merging. Please participate with the open mind.
I don't think it would work for the reasons I outline in my answer
The reason I like this site is because of all of the thought provoking questions related to the field of programming.
Many questions have involved design, but only when specifically related to programming issues. Answers to those questions on this site have involved things like "programming != graphics design". Additionally, many people have gone to great lengths to point out that the skills involved in design are a completely different set of skills used in programming.
Merging programming with UI would be like merging with Computer Hardware design, which also involves a completely different set of skills. Let's draw the line in the sand right here and keep this site limited to just programming.
At face value it sounds like a bad idea, but since most of UI is as subjective as is allowed on $this. It might add a little color to the site and I wouldn't have to go somewhere else to ask why my program looks like the Bruce Wayne's car stereo.