Following the discussion in T8686 and T8685 , alongside with @bshah we opted for creating a web site similar to the proposal of T8685. The web site is based on whatcanidoformozilla (many thanks to @IlyaBizyaev, I was not aware of this).
As soon as potential contributors navigate to the home page of the new site (or part of plasma-mobile.org), a set of questions will guide them to a phabricator task (which in turn have been revamped).
What needs to be done?
We have to create an hierarchy of question-answer nodes having as leaf-nodes the Plasma Mobile phabricator tasks. We have just started working on this here .
P.S. Since whatcanidoformozilla is licensed under MPL, I think that there is no problem publishing our modifications under GPL, shipping original files under MPL.