Oh, so that’s what you mean. That is already in our TODO list with the name "tagging rules". (I call them rules because dragging a tabble T1 onto another tabble T2 is equivalent to creating a rule that says "if a file is in T1, then it must also be in T2".)
But, if that’s what you mean, then I see no relation with the removal of categories. I mean, why did you not need such a feature when you had categories, and now you do? What is it that you could do when you had categories and you cannot do now?