How exactly changing a default that users rely on is going to make it easy to move away from it?

Instead of migrating to dotenv-ng, these users could be putting effort into migrating away from .env files entirely.

edit: I understand SecretSpec needs to parse .env files exactly like Node.js’s dotenv library, which doesn’t support interpolation, to make it easier for these projects to use SecretSpec.

I’m saying making this a standalone library is bad. Rust projects will pick this up and use it instead of SecretSpec, and users of the unmaintained Rust crate will migrate to it.