For as long as IPython used readline, users' .inputrc settings were respected at the input prompt.

This does not appear to be the case - as prompt_toolkit does not currently support .inputrc.

Can we add a note about this? I actually don't see anything in what's new for 5.x - only 4.x notes in there.

vi users will want to turn this off, or at least know how to turn on prompt_toolkit's vi mode (I think it has one?).

I get the impression that @takluyver @jonathanslenders seem to be closest to this.