Tags exist to help classify questions, both to help people searching for questions to find them and to help people intending to answer questions find the ones that they are interested in. An "elegant" tag would seem to serve neither purpose. For instance, a question asking for a more elegant proof of some topological fact is primarily a topology question, since it is of interest to topologists and requires familiarity with that field. The people looking for that question would have little interest in a question that was asking for an elegant proof of some number theoretic fact (and vice versa), yet the tag would put them together. Really, a question could have any mathematical content and still fit under this tag so long as it asks for something more elegant than the usual proof, which means that the tag would be doing very little to classify problems.