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My proposalNot the complete thing, this is just the front. The rest looks like the standard GC controller, maybe without the Z-button.
Gray: Analog-Pad (analog stick with wide hat to feel like a pad), Start, Select buttons.
Light gray: LCD-screen.
Red: Trackball
Green: A-Button, clickable digital coolie-hat.
Yellow, Cyan, Blue, Purple: B, C, X, Y, Z-Buttons.
Maybe the exact shape needs tweaking to feel more comfortable, but it shows what I'd like on a controller. If I could do it I'd build it myself just to try out how it fits PC-gaming...