Right now there is no way to specify the required Flutter version in the pubspec.yaml. One should be able to pin the build to a specific version (or commit) of Flutter so that the build is reproducible in the future. Furthermore, there is no way currently to ensure developers working on a shared codebase all use the same version of Flutter, making collaboration on bugfixing and debugging potentially impossible.

tl;dr it would be nice if it were possible to specify the version of Flutter to use just like one could specify the Dart SDK version to use.