According to the legend, there was such a plugin. There were some complaints from people, though, regarding a couple of bugs. Maybe they had been fixed. Here is the post: http://www.question2answer.org/qa/31733
It seems the only link to the plugin is this one, as the author has removed the file from his Dropbox: https://github.com/ProThoughts/q2a-hashtagger
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May 7, 2020: Q2A 1.8.4 released!