1. The plugin system is currently not public so there is only the iCUE and Chroma plugin for now, it's something that's on our long-term roadmap. #2 Showing 1 - 2 of 2 comments.
2. I have been able to get the Wallpaper Engine's visualizer working from time to time, but I don't know exactly how I've been doing it because the process has been different each time, I believe. Also, it always reverts back to iCUE's RGB settings, either after awhile, restarting the computer, or waking it from sleep mode.

Wallpaper Engine 1.6.10. With the Wallpaper Engine app, you can literally bring your desktop to life. This software allows you to replace static desktop wallpapers with animated ones. Among the supported formats, there are both 3D and 2D animations, as well as websites and video streams. Thanks to a wide set of settings, Wallpaper Engine can be.

So I just finished up my latest plugin for Rainmeter, Message Passing. The goal of this plugin is primarily to allow for back and forth communication with Wallpaper Engine but I named it more broadly since it could be used for other things.
It has full support for multiple websocket addresses and multiple connections on each address. You can run commands on websocket Open, Close, and Message (Can even use dynamic variables). Get clients connected to each measure from its decimal value.
The options for the Measure are:
Name - Name of the service to run, adds / to the beginning if you do not.
I recommend using unique names if you only want your info. So a name of tjMusicInfo would get a url of ws://127.0.0.1:58932/tjMusicInfo in the program you are communicating to
Port - Port to use, is ignored right now and is always 58932
OnOpen - A rainmeter bang to execute when connection is first made
Note: Will not fire if connection already existed and was opened when your websocket is created

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OnClose - A rainmeter bang to execute on connection being closed Note: Only fires with the connection is closed, does not fire if it never opens

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OnMessage - A rainmeter bang to execute whenever a message is received with your service name
Note: Add $Message$ to the command to have it be replaced with the message contents
You can always find the latest release and keep up to date with the plugin here: https://github.com/tjhrulz/MessagePassingForRainmeter