Absolutely agreed. One limitation of the Iron Triangle concept is that it often seems to be used to make decisions based on a snapshot in time (i.e. which two are we choosing now), when some choices have longer half-lives than others.

S. McConnell adds an interesting take on this in his: Brooks' Law Repealed? article.

user innovation toolkit - a product malleable enough to let users adapt it to their own needs.

Trello is a project management tool that provides boards, lists, and cards. The cards represent tasks or items, and move across columns on the board as they progress to a new stage of development. No particular method is prescribed. The individual or team decides how to use Trello, and the method is likely to evolve. Different projects may require different methods.

Trello has an API to allow automation and customization. After agreeing on how to use the board, different team members might use the API to build interfaces that work best for them.