The new ColumnTransformer allows the user to specify column names or indices. I think it should be possible to specify a set of columns as a function. Indeed, towards #10603, we should probably have an inbuilt function that distinguishes between categorical and numeric pd.Series dtypes.

In order to support the remainder functionality, I believe the function should have signature: (X,) -> column indices where column indices is any of the supported column specification formats.

Sound good @amueller, @jorisvandenbossche?