I think I know what you mean. 2 years ago I wrote a horribly long post here and have suggested something similar under point A.2)
Although I still stand behind the proposal and mainly its reasoning, in the meantime I believe that it would be enough if bear would allow typing tags by autocomplete inside the search field of articles list. See here
What also could be added in terms of functionality: A command “Add tag to search” in the context menu of the tags in left pane