This is a different issue - if you require 1.index.js from another index.js file, you need to compile index.js so that everything is packaged within one file. Dynamic import of JS files won't be supported by the plugin system.
Also, you might want to consider unpacking each plugin into its own subfolder under cache to avoid name collisions when multiple plugins have e.g. 1.index.js or some other file with the same name.
Yes that's how it already works.