Since we want to have a Comment feature which is very similar to how Facebook functions, it can be used as a chat. The main difference in a chat is that messages scroll up as new messages appear. This can be achieved with the comments by placing them inside a frame with a scrollbar.

Therefore, once our comments are made to update in someone else's browser (i.e. user A writes a comment, then a few seconds later user B sees it!), we in effect have a chat. The only thing would be to offer a way to reduce the resync delay to make it more appreciable as such.

See: Comment feature

See: AJAX feature (Inline Editing) [core]

See: Auto-cross computer update feature