The 90° isn't the big problem with traditional notation. It's that the same note in different octaves looks different. It's as if in programming you wrote a for loop differently for every level of nesting. The new notation draws against the same pattern of staff lines for each octave; plus, you don't have to remember sharps and flats from the key.
I've long wished for these two improvements, especially the first one; OTOH I'd keep the traditional whole note, half note, etc., for precision and concision -- the piano-roll style feels more like training wheels.
Regarding remembering flats and sharps... That may be easy for beginners, but it's actually not good. You do have to remember the sharps and flats because you have to know in which key you are playing to see where is the music going. And when you're playing you end up not needing the flats in each note because they're always there. They end up being redundant, so by removing them you gain simplicity and you can see more clearly the flats and sharps that actually matter and change how the music sounds.
Notes in different octaves are different and hence should look different. Even if you restrict to keyboard instruments, I am not sure you describe an existing problem with classical notation.
For the non-keyboard instruments I know how to play, tones in different octaves having different identifications is a must unless you want to add extra parts to the notation.
I think the point is that the standard clefs would be better aligned if there were 6 lines instead of 5, so both bass and treble could be EGBDFA. It would put the low C one below the bass clef and the high C one above the treble clef, instead of two below and two above but only one in between.
Yes, that was my general thought -- (added:) but that still would have two octaves different, where a note between staff lines in one octave is on a staff line in the other.
Also when you go above or below the two clefs and draw ledger lines for those notes, you're losing the background pattern once again -- you start having to count notes. With this proposed notation you'd draw another background octave (or enough of it for the notes used).
I've long wished for these two improvements, especially the first one; OTOH I'd keep the traditional whole note, half note, etc., for precision and concision -- the piano-roll style feels more like training wheels.