It's a follow-up to FOSDEM.
We need a "Pipeline Debugger", which would allow to easily attach to Pipeline, setup breakpoints and to check Pipeline context in them. Other common debugger features would be useful as well.
Both in-Jenkins and external-IDE implementations would be useful.
Related Jenkins 2.0 contributor summit notes: https://docs.google.com/document/d/1yK2J_sv1ceLYYbeLzEW8VZ3HEr8AxZcZr8GhMk6gLUY/edit#heading=h.wif2w2yslznh