Preview for updates is also a required (well, highly desired) feature for moving forward with storing node update history to resolve the problem of people blanking out their own nodes in regret, making silent updates that make some replies appear nonsensical, misguided newbie updates that wipe out the original question, etc.
It's been desired for a long time. It is just a matter of someone tackling it. I've heard reports of people intending to take the task on, but I've yet to hear of any progress, despite some of the claims having been made a long time ago.
