I just realized this is quickly becoming far beyond the scope of a single feature, so I will start with what I think might be an MVP.

Single Feature Level

I would like to be able to select a note in the timeline and manually input a numerical value for its base frequency.

Ideally, I would also like a visual indication that this note is no longer snapped to the piano roll's intonation.

Scenario level Request

As someone interested in how subtle differences in intonation affect the feeling of harmony, I would like to be able to craft my own microtonal scales and use them on the timeline notetrack interface so that I can easily make music with a greater variety of options for harmonic expression.

The current state: The notetrack interface only allows me to select notes tuned in just intonation. If I want microtonal voicings, I must manually adjust the tuning of the synth I'm using. If the synth I'm using is polyphonic, I must create a second, third, maybe more synth, one for each simultaneous voice, and manually adjust the tuning of each one.

My dream state: I can create a scale myself of any selection of any size of arbitrary voicings and select how each note is displayed on the piano roll (E.g. black key vs white key, what the name of each tone on the scale is).

I can define how notes in one scale map to another scale.

I can select a block in a notetrack and set the scale it uses to any one of my scales. Any notes already in that block may be mapped to their respective position in the new scale using a mapping of my choice, or I may choose to preserve the old intonation. Notes without a mapping are unaltered, but have some visual cue to represent that they are not locked in to the scale.