I didn't play with the HN API but I wonder if it's possible to post comments using the API. I haven't seen any program support user comments, it would be neat to be able to post comments using vim :-)
It's not currently possible to post comments using the official API (or any of the unofficial APIs), but this probably wouldn't be difficult to implement using a standard POST request to the actual Hacker News web server. The harder part would be getting the interface for posting comments inside of Vim user friendly; it would probably be similar to how fugitive.vim lets you enter git commit messages.
I will definitely look into adding this to the plugin if enough interest is shown.
Maybe @dang would be kind enough to let us know if we'll ever be able to use the API to post AUTH and post comments.