Of course, but in the binary case, `LabelBinarizer` returns a vector (1-d) of booleans while `predict_proba` output is returns an `n_samples` × 2 matrix. We'd have to document that special case and handle it regardless, so it wouldn't be a win in terms of code simplicity or ease of use.

Inconsistencies have crept into the scikit-learn API, and I'm dealing with them here so the user doesn't have to :(