For anyone interested, the main author (if I understood properly) did a presentation at RustNL on the UI aspect that was quite impressive performance wise : https://youtu.be/rC4FCS-oMpg
Technically, that talk is by the author of the UI system/IDE that uses the synthesizer as an extended hello world. The synthesizer itself is by a different guy ( https://thisisnotrocketscience.nl ) who's been calling his bassline synths somethingmetallicfish since almost forever.