Asynchronous updates/notifications

For some long-running operations, it would be nice if a server could send asynchronous notifications to a client, so the client doesn't have to poll (or refresh periodically) to get progress updates.  I'm wondering if something similar to the 100-Continue mechanism could be used for this.  Maybe with a new status code like 101-Notification.  A client could send an Expect (or Accept or similar) header to indicate willingness to accept notifications.  A server could send any number of interim 101-Notification responses, with message-bodies, before sending a final status code.  101s would not be sent until the entire request arrives.  

Comments?

    -Carl Kugler