(Switching it to the ee-list)
We may even want to try using it for remaining Echo tasks as well, not just for Flow.
I'm against changing things mid-stream. Let's see if Mingle works out for Flow (which hasn't started), and then we can see about its use elsewhere. Trello has worked out very well for E3 (as well as being valuable for the early development of Echo), and I'm not mandating E2 be backporting its use to Page Curation. ;-)
At the end of the day tools like Mingle, Bugzilla, Trello, Gerrit, wiki… are secondary documentation. Primary documentation is the code (git), followed closely by on-wiki for people who don't speak the language of code (when you think about it, that is part of our vision statement).
There is a cost to using secondary documentation, that means it has no value for its own sake, but only derives its value to the extent it helps in the creation of the primary forms.
Once a project has reached a certain level of maturity, any unnecessary documentation can be disposed of. Our process as it stands today doesn't allow us to be free of things like Gerrit, Bugzilla or wiki, but being able to let go of the unnecessary should be our goal. I like to think of these tools like writing on a napkin, it's okay at a certain time in the development process, but I wouldn't want everything we do to require a napkin doodling before implementation. ;-)
In the case of Mingle/Trello specifically these are closed source (possibly externally-hosted) software infrastructure pieces that we, as a Foundation, do not want to have an ongoing dependence on. During project creation and early development, the deadline-formation and other management tasks these afford are sometimes necessary in commercial space but do not really exist in all-volunteer open-source efforts, so some degree of dependence when there aren't open-source solutions becomes a necessary evil for that time in our project development. However, an ongoing dependence on these tools would become a wall prohibiting certain members of our community from being able to fully participate in, and that would be contrary to our commitment.
Take care,
terry