Whispering - Better than Private Messages?

This springs from the discussion on Drupal regarding integration with Vanilla. One developer asked what Vanilla used that Drupal didn't, and while most of the responses are theming-oriented, one thing stands out: Vanilla's unique whispering system. Simply put, this is the reason that I wouldn't ever use a Drupal forum as opposed to a Vanilla one. It's also why I've recently stopped using vBulletin, which is big considering how much those guys charge for their stuff.

Simply put, Whispering is private messaging carried across comments (forum posts). A PM is essentially a basic node that nobody else can read, right? Whispering takes this a step further, letting you post individual comments that only certain people can read. This lets people talk privately about a node (forum thread) without disrupting the conversation.

Here's what such a module would do, I'm guessing, for Drupal to work.

1) It would add a field to all nodes and comments: (Whisper Message To).
2) Nodes created privately would not appear at all on the main page.
3) New comments on nodes that were whispered would not appear as new comments in terms of bumping for users. Only users being whispered to would see the topic bumped.

That's all that would be required for a default. Other things Vanilla does with them (not essential, but still very nice) include:

1) Reply buttons on whispered post that prepopulate the whisper field with the original whisperer's name.
2) Special highlighting to point out posts that were a) whispered from a user and b) whispered to a user.
3) A block shows recent whispers to a user (like a PM inbox, though a bit more versatile).

And features that Vanilla doesn't have that would still be nice:

1) Whispers to multiple people at once.
2) Filter conversations in order to ONLY view whispers and not the main thread.
3) A central page to show all whispers, perhaps sorted by node type.

I think this would be a very useful feature that would replace the aging private message system. Would anybody else think this would be useful? (On the Vanilla thread on Drupal, one person said that they couldn't imagine why this would be useful - I would argue that both admins and offline friends would find this to be a very useful feature. And Drupal, after all, is about progress. Not just adapting to standards that are 6 years old.)

-Rory