Use case

For devices, without GMS we want to override the default implementation of packages like firebase_auth.
To achieve this we want to implement the firebase_auth_platform_interface and use our custom class.

Proposal

In the federated plugin proposal by @amirh, there is a section about overriding the default implementation with a custom package:
https://docs.google.com/document/d/1LD7QjmzJZLCopUrFAAE98wOUQpjmguyGTN2wd_89Srs/edit#heading=h.zc9ie62xv82k

We thought something like this should be possible:

pubspec.yaml

dependencies: 
  firebase_auth: any
  firebase_auth_android_rest: any

And because the Flutter tool knows that firebase_auth_android_rest provides a custom implementation of the firebase_auth_platform_interface/firebase_auth package, it uses firebase_auth_android_rest and not firebase_auth for Android.

We don't know if this is possible yet.