I agree with the sentiment, however it is currently possible for BUILD methods to do useful things with parameters that were passed to the constructor but don't correspond to any attribute names. MooseX::SlurpyConstructor is an example thereof. So if any such feature were added to Moose, it would have serious backwards compatibility problems, meaning that realistically it would have to be opt-in, and thus not especially different from the current situation where you opt into strict constructors using MooseX::StrictConstructor.