The accidental spacing is a good tweak. Those rare cases you mention are rare indeed! They might happen more often in microtonal music (which is itself rare), in which the “enharmonic equivalents” are actually different pitches.

The main drawback I see is that it would make notes and intervals harder to learn and recognize because their appearance would be less consistent. I would rather have greater consistency. You just have to shift how you think about the diatonic scale, no longer as something that needs to be ‘built-in’ to the staff (as in traditional notation) or the notes (as you’re proposing) but as a particular pattern of intervals that you learn to easily recognize (see Scales). Making the interval relationships as clear as possible is the top priority, and then the diatonic scales and the rest will follow.

Another way to put it is that whether a note is black or white is a very obvious, vivid aspect of a note, probably the most readily apparent thing about a note. Wouldn’t it be better to use this to help distinguish pitches and interval patterns than to “waste” it on just indicating accidental notes? It is already easy to tell if a note is an accidental because it would have one of TwinNote’s alternative accidental signs.

Instead, On F use a UPWARD triangular white note. So E has a downward white note and F has an upward white note on the same line. This means a simple C major scale is all white notes with those below F point down and those above E pointing up.

What this means is that diatonic melodies will all be white notes in a very compact way and it also becomes easier to distinguish C D E from F G A B. Chromatic alterations are extremely obvious(black notes).

One could use a transposing system so that the order is always the same on different tonics. e.g., for whatever key we are in the half-steps do this flip-flop. This will produce diatonic melodies, regardless of key, to have all white notes.

Here’s my renditions of Fur Elise: http://www.youtube.com/watch?v=x-O0qb66AoQ

Thanks!
Tj
tjjazzpiano.blogspot.com