If you add an icons folder to your published node filled with images, they will automatically get hosted at a location (based on your config) such as mywebsite:1880/admin/icons/your-published-node-package-name/theicon.svg The icon will then show up in the icon picker. As a quick example, I added the coffee.svg to my mp4frag node and can then use it in my ffmpeg node.
For me, the image is directly linked at https://xxxxxxxxxxxx/admin/icons/@kevingodell/node-red-mp4frag/bmc-logo.svg.
Unless I am misunderstanding @dceejay, then I think you could make a node that has a variety of icons and other nodes can use them.
