Most of the time, I do not rebuild complex stacks from scratch, but rather start off from a certain "basic" version of my instruments. It would be super convenient to be able to select them from a drop-down, similar to the built-in presets.

The feature could be configurable over ~/.config/sointu/presets.yml. This file could have the structure

presets:
 - name: Single instrument
   location: /path/to/single_instrument.yml
 - name: Instrument in patch
   location: /path/to/patch.yml:instrument_name_in_patch

The tracker could display a button (or have a menu entry) to make the current instrument a preset automatically (by adding it to presets.yml).