I see your point but I feel that is a bit unlike the normal api.
By 'implies' do you mean 'looks like that to the user'? You could just set ``indicator_matrix`` to a different value before calling ``inverse_transform`` if you wanted.

The reason why I think it doesn't fit well in the API is that we usually haSove all parameters that don't depend on the data in as ``__init__`` parameters. There is a good reason for that: having parameters to the functions breaks grid-searching and pipelining.

So if someone wants to use ``Pipeline`` with ``inverse_transform`` you get into trouble.
For all other transform based methods, the parameters are always specified for ``__init__`` so as a user I wouldn't expect a parameter in ``inverse_transform`` now.