I see. You said above that a comment only has a day to make it out of pending. Why not auto-delete it when it doesn't? Edit: Never mind that question. Based on https://news.ycombinator.com/item?id=7446005 this seems to be the case (i.e., you won't have to delete a failed pending comment manually).
On a related note, the new system may prevent people from posting in the feature suggestion thread (https://news.ycombinator.com/item?id=363). Since it's already a special thread that never closes for comments perhaps comments posted there should not be made pending.
How long is the immutable timeout? I've never timed it, but I have a hunch that comments lose their delete-ability in less than 24 hours. So please be sure that pending comments can be deleted for the entire duration of their 24hr pend state.
I like the idea of pending comments, but I don't like encouraging the deletion of the unsuccessful pending comments. Especially in the low flow threads.
I suppose that the 24 hours is a parameter that is easy to change and tweak. I think it's a lot of time. What about 1 or 2 hours?
Another possible idea is to have up to two pending comments, so someone can contribute in two threads, go to work/eat/sleep, and read the replies. But this version is more difficult to implement and more difficult to explain.
You need to add a cool off timer of say 5 minutes still even if you delete a pending post, otherwise can bet somebody will abuse this to churn up there system DOS style. There be dragons out there.
Also some visiable indication on near the user/logoff part of the page indicating if can post or awaiting approval of a pend - say a "+" indicating can add a post and a "-" indicating you can't as have pending post.
