Impossible. Too many needs. Too many different ways of people to use their computers.
So the people will end up customising it (if they demand for "more"). Takes maybe an hour on a new install, then the machine runs for some years. Yeah, it actually gets work done.
Let me compare computing with car racing. Of course you can drive as it is, but your performance will improve, if you set up everything correctly (gears, aerodynamics, engine, tires) to fit your driving style (and the track). And if you want to get the maximum out of computing, you'll end up tweaking and customising.
Target group:
Salix/Slackware for average computer users (that don't ask for "more")? Difficult. It was far too often about one popular closed-source application, that didn't made it to Slackware... so you had to compile it... so FORGET IT! And then ten different loud nerds shouting "I like", "I use", "I prefer" so that's your target group here.
Xfce:
You are a radical design-terrorist and will not bomb my old-fashioned castle (Xfce)! Allright, you get a try. What would you critisize on an Xfce desktop? It's a (computer memory) efficent desktop, and I could have brought two of my 32-bit machines to the scrapyard already, if there wouldn't be Xfce around.
Catapults ready...