Very cool! I'd recommend changing the default oscillator. 1000hz sine wave becomes aggravating extremely quickly! Maybe 500hz (lower?), and 0.05 gain? Or at least a filter after the oscillator.

But I really like this idea - you could take it much further (I'm sure you plan too!) From a UX perspective I think most people will run quickly from this page, because unless you understand modular synths it will be very daunting to figure out how to make something that sounds nice. A dropdown with some defaults would at least let them play to get an intuition of what's happening.

I'd also make it easier to see how to add nodes - it's quite unintuitive at the moment. And a panic button to stop/play sound... The more I tried to make the sound quieter, the louder I accidentally made it!

But again, super cool idea - it would be great to make a SFXR/BFXR-type sound effect generator that would spit out web audio code!