1. There should be a global play/pause/reset on the top or bottom of the page, and also a main volume knob. It takes some work just to figure out where the patching starts and ends.
2. You should have a bunch of well-named presets for newcomers to get a feel for what it can do and also use as starting points.
3. The volume "sliders" look like level meters. The first impression is that everything is on max volume constantly. Probably better to have a physical-looking slider. On that note, it would be nice to see the current output of each CV port. It could be just a fading LED if you want to stay "realistic".
A separate question, did you consider porting VCV (using emscripten) instead? If so, why did you choose this route?
Patchcab started as an exercise for myself to learn the basics of modular audio and music theory. Working with tools I already know seemed the best idea and the Tone.js was a prefect fit for this. The exercise then turned to an idea of a modular (code and audio wise) Javascript/Typescript synth that would resemble VCV visually. Porting VCV itself to a browser is a really interesting idea and has been done to some extent https://github.com/miRackModular/Rack, but is really out of scope for what I wanted to build :) That said, I feel like porting some open source Eurorack modules (Mutable instruments, https://github.com/pichenettes/eurorack, I'm looking at you) would be a really nice next step.
The only comment I do have is that I find it very hard to turn some of the dials. It appears as if my mouse action isn't registering properly.