Hi,
If the Pitch Stepper module in the Instrument Modulation page could be enhanced so that in 12-step mode each step could be used to tune each key in the octave. This would allow the creation of microtonal tunings totally natively inside Renoise.
U-he Zebra has a similar function when you assign its Mod Mapper into Oscillator Tune, setting step amount to 12 and mode to Key.