Bah, I personally dislike having multiple file types for the same file type. It just confuses people. Remember all the URL's you visited that ended with html and needed to end with htm?

But of course, if the official file types are all 4 (.adoc, .asciidoc, .ad, .asc) - which is not my decision to make - and that's not about to be changed, we should list all 4.