Again it sounds exactly like Jabber/XMPP. I really don't see this happening. If these developers really wanted to support more users, they could use a XMPP server and it would allow you to chat with Google Talk, Jabber, etc users. However, when you venture into becoming an IM system, then you will lose to apps like Beejive who have implemented these features already and are very mature.
perhaps minor for some - but the difference is that you don't have to be logged in. These BBM type messenger apps use push and don't require the program to be open or for you to be logged in...
imessenger right now will also tell you if the message has been read yet.
So it's a little different than just what beejive does.