The advantage of this PureData plugin and Max4Live over VCVRack is that you can edit the patch on the fly right in the DAW (in addition to the fact that visual programming is way more accessible than a compiled language).
Yes. There os also a commercial initiative by the author of VCV to have it as a VST im the DAW. The difference between the two are that Cardinal only accepts open source modules and is packaged with all of them, while the VCV official VST lets you download modules on the fly.
The fact that it's paid might be a turn off for some, but I've found it to be really useful, and it works really well inside of Ableton. Can't speak for other DAWs but having been using it for the past 6 months or so, it's been fantastic.
Does anyone know of good resources for folks who want to develop their own modules for VCV rack?
This is cool, but I think we are talking about different things. From reading the description of this project it looks like you can't actually _edit_ the individual modules. They still require compilation since it's C++. You can change the patch by adding modules and tweaking them a-la hardware Eurorack.
M4L and PD allow you to open the patch ("patch" as in MaxMSP patch, not a Eurorack patch) and edit its source code. Which is a completely different level of sound manipulation and synthesis.
It's all about the level you want to edit the patch at. With PD you are likely to generally work at a lower level than in Rack/Cardinal, but you're still patching together elements of varying complexity.
You can also run PD as a plugin inside Rack to get "the best of both worlds".