Agreed, Digikam is quite amazing, and I use it for my own collection---it implements everything I've ever wanted, and more, and is easy to use. I think it does most things our editor wants in the way our editor seems to want them to work, with one exception: it is very much album-based and therefore requires importing a new directory (though the imported set of files are not "black box", one simply gets a copy of the original directory and the files within it). And for importing, at least it defaults to the directory from which digikam was launched on the command line (that's frequently a big pet peeve of mine as well).
However, I wonder whether editor is looking for a more lightweight approach? If so, it's possible that gwenview may be a closer KDE equivalent: even though it's not really a "photo management application" it addresses, quite nicely, most of the things that made our editor grump about Shotwell. On the other hand, as far as I can tell it currently lacks features that he might find essential: viewing RAW images without needing to first convert to another format (at least you can do this conveniently within gwenview...), and photo-organizational features (I can't find a way to "display by tag," though as nepomuk matures I suspect that will soon come for free). So I doubt it would currently fit his needs. Still, it's surely an application worth keeping an eye on.