Dependency specifiers akin to PEP 508 from Python

[thernstig]

Problem

Often I want to install a package where I wished the package declared a subset of dependencies to be installed as well.

Python and PEP 508 solves this. See also https://packaging.python.org/en/latest/specifications/dependency-specifiers/#dependency-specifiers.

An example of this can be seen here:

pip install diffusers["torch"]

The ["torch"] part tells us to install diffusers with a subset of tools, in this case also torch.

A real-world use case

https://github.com/socketio/socket.io/ depends on the ws package. But the Node.js API now includes a WebSocket implementation of its own.

If I could then specify this:

npm install socket.io[no-ws]

I could skip that extra package and use the built-in one instead, without having to pollute my node_modules/ with unnecessary packages.

Is this a good or bad idea for an RFCS?