Suggestion: DAG Groups

Instead of a tree hierachy, perhaps groups would be better off based on a DAG - a Directed Acyclic Graph. This would allow groups to have multiple parents as well as multiple children. For example, ~mazda might have ~cars and ~japan as parents, and ~tolkein might have ~fantasy and ~linguistics as parents. I think this could maintain the benefits of the hierachical system while making it easier to find a group that suits the post.

While potentially complex, a good UI which effectively visualised the DAG to allow a content submitter to hone in on the correct group-node, and potentially create a new one on the fly if none was appropriate, could make this concept reasonably intuitive. This problem has already been tackled by creators of git GUIs, so perhaps some ideas could be adapted from that space.

One issue is that a node in a DAG is much harder to identify with a text string than a node in a tree-based hierachy. One solution would be that the submitter could choose a 'primary path' which would be displayed to readers, which, upon being clicked, would display the full DAG, including all the potentially numerous paths which would lead to that group-node. For example, I might choose ~linguistics.tolkein.quenya as the primary path, but upon clicking, the reader can discover that ~fantasy.tolkein.quenya and ~linguistics.conlangs.quenya and ~writing.worldbuilding.quenya all lead to the same group-node [edit: ugly illustration]. I feel that this solution could potentially be powerful enough to remove the need for tags entirely. Viewing the homepage of any particular group-node on the DAG would aggregate posts to all child groups, meaning that the effects of community fragmentation are mitigated. Even a post to a really specific group-node, like ~cars.mazda.mx5.na, will still enjoy the same status and priority to the readers of the ~cars homepage as a post made directly to the ~cars group-node.