Does this qualify it as deserving its own tag at this point? The numbers will certainly increase quickly judging by how many
identify-this-x questions we get daily and if they were converted over, identify-this-short would be the 25th most popular tag on the site.
I'm not sure such a distinction is really necessary, since short movies are in fact movies like any other movie, too. We in turn have a short-films tag that can be added to identify-this-movie questions, in the same way like decade or genre tags. While this of course requires effort from the asker to add that tag, this would be the same effort required to tag a question identify-this-short instead of identify-this-movie, and ID questions often need proper retagging anyway.
Likewise am I not sure if the identify-this-short tag might encourage ID questions about any kind of short, like YouTube clips or whatever questionable media.