Have you ever thought about an invention that maybe YOU can't make, but it sure would be nice if someone else did?
This is more about technology than about no one thinking about it, but I wish someone would invent a floppy pressure-sensitive sheet that could roll out on a drafting table and input drawings into a computer. Like the Wacom tablet, it would be a simple way to draw directly into a computer program, and skip the scanning step.
In this case, the tablet would be (obviously) much larger than the 4x6 to 9x12 area that most reasonably-priced tablets offer, and allow the artist to be more expressive with his or her arm movements.
Now, in the wake of the Cintiq tablets (large rotatable monitors that you can draw on with pressure-sensitive pens), there's the thought of making a sheet like the one above that doubles as a monitor as well. I'm sure people would make it if they could-- I can't imagine a graphic artist that wouldn't at least want to check it out.
You could use it as a regular desk as well-- it would keep your spreadsheets organized, and your desk could be laid out like mine is now ("I think that's in the upper right hand corner, under the tape dispenser") but with the help of a computer processor to keep everything organized behind the scenes.
Again, I know that people would invent it if they could possibly make it work and make it not cost ten million dollars, so don't worry, guys. I'll wait.