> Coloured note heads are better at conveying pitch than note shapes - which are already used in percussion notation.
Shape notes are used in singing traditions such as Sacred Harp and Christian Harmony to help singers find the right pitch. It works very well. I don't know if anyone uses them for instrumental music.
Then again, if someone came up with a new One True Notation, I can imagine someone producing a translator (like Google's augmented reality one) that takes pictures of historical scores and gives them back in the new style.
The grand staff is really a single giant clef with the middle line missed out for clarity, and some extra space added around it to allow for leger lines.
Your system would need extra legers above/below the clefs, so it wouldn't be an obvious improvement.
Coloured note heads are better at conveying pitch than note shapes - which are already used in percussion notation. But coloured note heads cost a lot more to print, and scores are expensive enough as it is.
Having notation that is consistent across all instruments, not just piano, is a good thing.
I doubt anyone would duplicate current notation if it was designed from scratch today. But like a lot of things - including CSS and HTML - it's a mass of accreted compromises with a massive existing user base.
No one is going to re-notate centuries of music with a new system, no matter how much more logical it is. It's not going to happen for the purely practical reason that most music will still be in the old system, and musicians would still have to learn that system to play it.