I wonder if a spread sheet-like mode of input would be better than free form text, sort of like excel. You could have one spread sheet on a tab for sequences, and another one on another tab for pattern sequencing. rows and column rulers would make a great way to measure beats.
If you are good at music, you should not need to hear each note as you enter it (although listening to it after you write it, to check for errors, is still helpful); even some composers could write music even if deaf; it didn't stop them!
I think this would be a terrible principle to design a musical interface around, though. A bit simplified, it's a bit like designing a counter for really tall people. As good as every musician and songwriter take hearing notes for granted
when writing; usually on piano, guitar, song or synth. They rely on it and would perform worse without aural feedback. You'd end up with Ludwig van Beethoven as your sole ideal user, and even then
-He had lots and lots and lots of training and was a professional composer hired by magnates to do one thing only. We're talking about hobbyists doing things in their spare time.
-While used as a fascinating curiosity today, he did so out of harsh necessity, not because he wanted to. A gameboy composer might just use LSDj.
-He had years of gradual degradation of hearing under which he was forced/allowed to build up this skill. An intimidatingly difficult interface would just turn people away for other options unless they have to use it.
-He wasn't completely deaf in the sense popularly envisioned until quite a bit later on in his career.
-Despite being well trained and a professional, his diminished hearing can be traced in his music. Gradually, he started to avoid using bright notes, until the time he got completely deaf. At that point none of it mattered, so the brights were included in his work again.
In his own writing:
"... Of course, I am resolved to rise above every obstacle, but how will it be possible? ..."
"... My hearing has grown steadily worse over the last three years, which was said to be caused by the condition of my belly..."
" ... Often I can scarcely hear someone speaking softly, the tones yes, but not the words. However, as soon as anyone shouts it becomes intolerable..."
And even if someone is that
good at music (unlikely), the interface is still impacting the songwriting. Playback helps a long way to remedy that in lieu of instant feedback, of course.