> Gaël, the question for you is: how would you suggest enabling a Pipeline to be
> used within AdaBoost, or enabling AdaBoost to be used with a Pipeline base
> estimator?

I don't know. I just can feel that there are a bunch of issue with the
pipeline API, that we need all to write them in a design discussion
document, accumulate usecases and someone brave needs to figure out how
to move to the next step.

This is what @amueller did with the scorer API. It was a lot of tedious
work. But after all this work, we got something that was much more than
incremental, and really helped solving a lot of problems.