I’ve also just started diving into pipeline. I think you can access pipeline._stage. I think the current documentation is lacking a lot of details. But the implementation seems to be readable and shows a lot of things are possible.
Thanks @Marc, looking at the code, _state gives you the instantiated Parameterized classes, where as _stage, gives the layout as in the documented stage method.
_states dict, can also be used to access any initialised instances