I was wondering if I could help out with the development of “Niagra”.
I’m a technical artist with a special effects hat. Last year I made a modular particle
system for Unity (Amps) because I found their stock solution too inflexible.
After UE4 became public I thought I’d pay an Unreal veteran C++ coder to port
Amps (I’m a C# guy). Then to my delight I saw Cascade 2.0 mentioned on the
roadmap.
I hope I could be of assistance with the research, planning and system design
aspects. I don’t know how much of that is done or how you guys intend to approach
this, but here are the main steps I took before I wrote a single line of code for Amps:
Use case breakdowns: Gathering typical tasks, common effects and stuff
where existing solutions are problematic. Looking for patterns, features that the
examples share.
Initial node set: Getting a preliminary list of nodes which can cover the
aforementioned tasks. This step helps determining the “granularity” of the nodes,
what combination of simple (like math operations) and more complex (RGB to HSV
conversion) would work best. Categories can be established to aid the creation of
the class hierarchy later on. (An early node set for Amps.)
Data and event flow: A high level look of how the system works. (Again, an outdated
chart for Amps.) Input data, order of operations, output data, main events, etc.
User interface mockups: What to show and how to show it to the user. What
the expectations are, what conventions should be followed, what specific UI elements
are be required, etc.
So that’s it, although I’m not sure how much of this fits your workflow. Still, I’d be
happy to push this along as far as I can for two reasons: Working on this would allow
me to learn a great deal, plus, well, I’d really like to use a next gen particle system. 
I’ll fail often but I will fail fast too so if you can give feedback (along with the
community) then we could start chipping away the workload.