Sometimes, certainly. I'm not sure it would work well as a general policy. People may rot13 things incorrectly, or may rot13 a post only some of which constitutes a spoiler. If that gets passed along to all further comments, it'll cut everyone who avoids spoilers out of the discussion. Your comment, for example, is interesting, and led me to look up Bane's Rule of Two, but I would not have done so if I hadn't suspected that yours was an incorrect rot13 to begin with.