For now you can use inter-app MIDI and audio to use it as an external instrument in most DAWs.
I use it with RogueAmoeba's LoopBack (like SoundFlower, but less glitchy and way more flexible), and feed that into a composite audio device in the Mac's Audio MIDI Setup app. That gives me a stereo pair for assignment in Ableton's external instrument.
This is really not that cumbersome to setup. Once you setup the inter-app config, you never have to change it. I created an External Instrument preset in Ableton with the corresponding MIDI out and Audio in, so it's really just a two-step process to use it: Launch VCV Rack, and load the External Instrument preset.
Seems like a great project and very finely polished! However it's too cumbersome to have to route the audio to be recorded.
For another open source modular synthetizer, there's ams: https://objectivewave.wordpress.com/ams-lv2/, https://github.com/blablack/ams-lv2
You can also extend it outside of regular emulated voltage controllers: http://drobilla.net/software/ingen