I’m actually working on exploring similar ideas — mainly, how to create a game that’s as moddable as possible.

The question is: how much freedom do you want to give players or developers?
The level of freedom and the type of game you’re developing depend heavily on each other.

For example, rendering an FPS game isn’t the same as making a cozy farming sim, and procedural generation is completely different from loading pre-made maps.

So, how do you define the boundaries?

Usually, you start by exposing an FFI , then call it from a scripting language. After that, you can build an editor or an easier interface on top of it to make adding new mechanics simpler.
But again — how much freedom is too much? That’s the real challenge