It has been proposed that needkey be a simple event. In this case, it would not provide any indication of the key that is needed and the application would need to call generateKeyRequest() to get an appropriate message or identifier, including for the Clear Key case. Such a change assumes that the consistent flow option is selected. See this example for an illustration of the impact of this change.
(Because sessionId is not included in needkey and is not generated until generateKeyRequest() generates a keymessage event, this cange would not result in the loss of any correlation. See Session Correlation for a discussion of the general lack of correlation.)
See http://dvcs.w3.org/hg/html-media/raw-file/tip/encrypted-media/encrypted-media.html#issue-needkey-simple-event-example for the possible impact of this and other proposed changes.
We should prioritize resolving this since it affects the basic API.
The needkey event signals that a key is needed and that any initdata necessary is available. Since generateKeyRequest moved to createSession on the MediaKeys object there is no longer the opportunity for an out of band mechanism to provide this initData to the CDM. I propose that this bug be resolved WONTFIX since the O-O changes make it no longer an option.