K has alot of addon apps to address what you're thinking of already.
But the strength, and weakness, of GNU/linux is the development process. Yes, you can do it, with alot of work. But that is also why worms/virus are so rare for this OS too. Every system is different..Different daemons running, different compilers, different system setups..enough so, that any thing written for one particular setup won't work on another. By the same token, setting up programs, etc, would run into the same hassle.
Would it be worth it? I don't know. For what I use my X environment for, KDE does a fine job. I can copy/paste, have enough apps to do what I need.
Do I want an Apple clone? No. By the same token, I don't want a Windows clone, either. I like my GNU/linux/Xorg the way it is. If I want to add something, I will. I don't want something that was made in committee, by someone else who "knows what the public wants". KDE even makes my skin crawl a little by the amassed amount of 'candy' that is in there.
If you think you can build a better Desktop Environment, go right ahead. But you are still going to butt your head against the inherent design attributes of GNU/linux. Installing will not be easy. Plug and Play will be difficult, at best. Drivers for hardware will be difficult. And every system is different. You may not have the right dependencies, for example.
RedHat tried....Now it's Fedora. Lindows tried, Didn't work out so hot. Your best bet is to try your own distro, so you know what is in it. As far as making a do-all-and-be-all desktop, good luck