Any reason comments is private with no setter?

I can form and submit a pull request if you'd like, but I'm wondering why the $comment array is private, with no setter.

Locally I added a setCommentVariable($key, $value) { $this->comment[$key] = $value; } for setting some extra things (which it sounds like Akismet encourages?)

For example, $akismet->setCommentVariable('comment_summary', $summary); and I also have comment_keywords which I submit.

Also, reading their blog, http://blog.akismet.com/2012/07/20/pro-tip-testing-testing/

There are some parameters such as user_role, or is_test which are useful. So, I'm wondering if exposing a setCustom($key, $value) or something similar might be worthwhile. Thoughts?