I noticed that functionality for sending notifications is now available with REST using

 http://api.myspace.com/v1/applications/{applicationId}/notifications

 But these are for existing members only, as far as I understand... But what about app invites? Is that still not available through rest, and if not, are there any short term plans for that, or must we still resort to OpenSocial for that?

 We have a forum devoted to this subject, you should get some good info there:

http://developer.myspace.com/Community/forums/81.aspx

I see.

 If it must be OpenSocial then, is there any way to use the OpenSocial myspace functionality in a MySpaceID application?

What I am looking at is the ability to invite friends from MySpaceId application.

Another vote for you to add this to REST