For the QC, a Kernom Ridge style parametric overdrive would be great. It seems like every feature-rich modeller should have a highly tweakable overdrive engine capable of dialing in specific clipping, saturation, and EQ character.
As a compliment to a Kernom Ridge, a built in oscilloscope would be amazing to be able to visualise the impact of the parameters. It would also be great for analysing waveform clipping and frequency response in existing presets! However, all thoughts welcome on whether it’s a block in the grid or a utility tool like the tuner, and what the interface might be.
For reference, the Korg NTS-2 Oscillator has all the right features.