I think it would be useful to have a way where you can have the same task exist in different boards, so that when you update a task in one board, it updates in all the other boards. The “mirror column” feature doesn’t work for this, because you would still need to create a new item, then link to the existing item. The @mention feature doesn’t work for the same reason. Tags only help to an extent, but they are not easy to organize.
A solution would be to be able to create a board that shows only items with a specific tag. Or to be able to assign different boards to the same item.
For context, I manage a team and client accounts. I need a folder for each client, as well as a folder for each department so that the hundreds of tasks we handle each week are organized and easy to find. So, for example, if I have a design task for client’s X, I need this task to exist in the client’s board, on the design board and on the “Tasks” board. If the task is updated in one of these boards, it gets updated in all. Similar to how you can add several tags to 1 item, you should be able to assign several boards too.