At least as of SLEP018, scikit-learn supports dataframes passed as X. In #25896 is a further place of current discussions.

This issue is to discuss whether or not, or in which form, a future scikit-learn should depend on narwhals for general dataframe support.

+ wide df support
+ less maintenance within scikit-learn
- external dependency

@scikit-learn/core-devs @MarcoGorelli