I didn't really find this thread on SO useful. Maybe the feature has been discontinued and/or because the thread is outdated (2014).
However, I have found a temporary solution, which might help address the problem for the time being. As @amoeba has mentioned, this is a very common problem, and displaying tag excerpts would really help people while editing questions, for tagging and untagging relevant tags.
Upon clicking on a particular tag, it gets flattened and then the excerpt gets displayed, as shown in the screenshot below (<-- which have been captured today 02 Sept. '15)