I cannot find any information on this now, but will it be possible to do activity requests over REST, not just JS?
The point being:
Case 1. User A does something on the service through MySpace, and an activity notification is sent to user B.
Case 2. User B does something through some external mechanism, but related to their MySpace relationship to user A.
The JS activity API can answer case 1, at least to some extent, but not case 2.
Though I wasn't getting into specifics, as they aren't critical to the discussion, I'm also not asking as an abstract thought exercise, there are some concrete reasons for apps to do this. The app I am currently working on has a few of them.
While hazarding referencing a competitor, I'll say that what I am mentioning is the equivalent of facebook.notifications.send. By the use of a session key, (and the rest of their auth scheme) an application can make an authenticated request back to Facebook on behalf of some user, but out of band of that user's direct interaction with the application on Facebook.
Does this sound possible in the plans for the activity API?