keystring I scribbled out some music on the proposed system you outlined. There's a problem, in particular for piano, when you get to where currently we have middle C. In the current system there is a symbolic overlap: The note "on" the first ledger line below the treble clef; and the note "on" the first ledger line above the bass clef, both denote the same note, middle C, and in the vicinity of those notes you can travel seamlessly. It provides a continuance. We lose that continuance in the proposed system.
In fact I don't think that would be a problem. In WieWaldi's proposed system, the continuance is at the note D, being on a space at the same distance down from the bottom line of the top clef (1 1/2 spaces) as it is up from the top line of the bottom clef.
Fun fact: there is already a clef that is exactly two octaves above the bass clef: the French Violin Clef. This is what it looks like:
It can be found in original French scores from the 17th or 18th centuries (Couperin, for example), but all modern editions have replaced it with the now standard treble clef.
If you want to give it a try, here's what the beginning of the last movement of Beethoven's op. 2 N° 3 looks like if the treble clefs are replaced with the French violin clef:
I actually can't find any real downside to this system. If this clef had become the standard, instead of the treble clef, I think it would work just as well not only for piano, but also for other instruments. There's one more ledger line to deal with at the bottom, but this means you have one less at the top, which doesn't seem a bad idea.
But would it be worth changing the present system and replacing it with this one? I would say, definitely not!
- You'd have to make new editions of all existing music. A gigantic undertaking. The confusion between the old editions still being used, and the new ones, would be dreadful.
- All musicians who had learnt the existing system would have to learn a new one. I can imagine that especially the learners who had just finally "got" the treble clef would be very unhappy indeed.
I think that the only people who would benefit from it would be the new learners. And I think that that benefit would be very slight.