I really enjoyed this sound toy for as simple as it is so far! The sound and visuals are imaginative and inspire a lot of ideas for potential interactions and features. Maybe the frogs transform over time, or have a way to hop to different steps in the sequence. I also like the creepy/uncanny angle a lot, and I imagine some adding hidden or gradually revealed interactions or supporting more unhinged sound possibilities with features that facilitate dissonance or extreme/uneven rhythm - even without equally uncanny visuals - could really bring that forward.
On the issue of continuous versus quantized pitch, I still quite like the continuous sliders because they tend toward more dissonant, out of tune sequences that are uniquely expressive in that uncanny way. But as you mentioned in your postmortem, quantization is nice for quality of life and being able to choose a scale could add variation, but I'd also suggest experimenting with non-equal temperament tunings or just general detuning on top of a quantized system.
Anyway, I think this is a really strong prototype and would be excited to see you add more!