I've tried using Houdini which was very powerful, but was put off by the "visual node builder". I'd like to be able to do something similar, but purely using code.
Blender is also open source. I suspect a combination of Blender, Sverchok and your own code driving them both would be close to what you ask for.
I'm interested in real-time, interactive stuff so I'm doing similar things in Unity. Unity allows scripting and customization right down to close to the metal and the UI is extremely amenable to customization as well. Tools such as Archimatix show how far you can push this: https://archimatix.com/
I'm currently working on procedural geometry and I keep flip-flopping between a simple and fast UI (very creative and intuitive), a node-based UI (slower but powerful) and a purely code-based interface (a weird mixture - powerful, sometimes fast and intuitive and sometimes not). I don't think node-based UI's are inherently bad. It's just hard to make them not suck and I know of very few examples that aren't plodding, inspiration killers.
But code is equally hard to make fluent and inspirational. Discoverability is poor and to do creative "live coding" you need to have a good memory, a great API, awesome autocomplete and a degree of luck.
So I'm developing 3 different interfaces and trying to understand where the sweet spot might lie. Maybe I'll be able to whittle it down to one interface eventually. ;-)
A quick prototype of my "fast" UI is here: http://www.polyhydra.org.uk/media/fastui/ Entirely keyboard driven at the moment. Crashes a bit too much but you get the idea. I'm currently refactoring the thing to be more useful as a code library as well: https://github.com/IxxyXR/polyhydra https://github.com/IxxyXR/polyhydra-upm
probably your closest bet imo. they're honest about the strengths and weaknesses, and while it doesn't have all the conveniences of commercial packages, the script node is there and can bring everything in sverchok and blender to bear in python.