The idea is to add a new mode to the key tracker, that would allow tracking the pattern effect portamento and vibrato commands.
How should it work? Currently when a key is hit, it is translated into one of the discrete steps in the output range. The new mode should respect portamento and vibrato calls, and alter the output value to reflect the amount of pitch modulation done by outputting values between the discrete steps, so a portamento of 50 cents up, should produce an output value right in the middle of the last triggered note step and the step that belongs to the note above it - deriving the data from the calculated pitch that a sample would have after issuing the commands. Another toggle mode might be desirable that would control how the portamento would react when crossing the output low/high limit values, i.e. to continue beyond or to stop/clamp at the boundaries.
A possible way to implement it in a non-breaking way would be to add a parameter to the native key tracker effect device, that when enabled would yield to the upgraded behavior. The modulation note key tracker device could also be upgraded by such an option, enabling the use of portamento for the comb and ring mod modulation filters.
Use cases would be various, from simple things, like filters shifting not only to the note played, but also to pattern effect portamentos, up to enabling the use of pitch pattern effect commands within techniques like using keytracked and tuned ringmods, comb filters or other tunable (modulation) effects. Currently such sounds are limited in that pattern effect commands have no influence on them - the new mode would enable such sound design tools to be controlled by pattern effect commands in sync with samples playing.