Please, raise your hand if you'd like:
The color syntax highlighting could be done in a couple different ways. KDevelop could do specify the individual entries in richtext, but the interface would have to know that it is doing so and render it accordingly. I am working on katepart's KateCompletionItem (subclasses QListBoxText currently) to see if I can get it to render richtext. Another alternative is to have the interface entirely responsible for highlighting. Presumably katepart could do this, but the highlighting might not be as rich since KDevelop knows more about the C++ syntax than Kate.
Regardless, I think these things would be pretty cool and it'd be nice to have them before KDE 4, but I don't know. Perhaps if enough hands are raised... :)