I think that the docstring should explicitly state that this option is useful for multioutput.

Also, I don't like the name of the option (both keyword argument and corresponding value). Indeed, it's not really a question of choice of weights, as only uniform is used. Thus it is more a question of averaging or not. Technically, there is nothing false in the current formulation. It is just very far from the intended use case, and will not very discoverable by the users.

From what I understand of the usecase, I think that I would call this 'multi_output' with True or False as possible values.