The way it works to post and update an action is that you post a new topic as usual, but you then tag it with new, blocked, current, done or discarded as things progress with the task. I propose that we use them as the follow up to team calls so we get posts that have at the top task descriptions or action points, and below a summary of the discussion so people have the context behind it.
Of note, moving tasks from one state to the next is done comfortably with drag and drop in the Kanban board. You can achieve the same by manually changing the tag – that’s also true.
The point with Kanban boards is to move items between them with drag and drop, like PostIt notes. That would not happen with themes / keywords, as Discourse topics don’t suddenly what they are about. For what you want, a list of normal Discourse tags seems sufficient to keep an overview. Note that you can subscribe to Discourse tags just as you can to topics an categories, to get an update when a new topic is tagged that way.