A score by This Is My Next: some very possible last-minute iOS 5 details. It sounds like exactly what you're hoping for and entirely what you're expecting.
Namely, native BBM-style messaging using Apple's "own MMS/SMS protocol which will be a native part of the phone" that'll identify iOS users and "route the message accordingly". Anybody hanging on to BlackBerry for BBM has one less reason to stick around.
Notifications apparently are "more like a white, gradient Growl notification", with a master pulldown window, a la Android. And that pulldown window is where widgets will live. Finally, there's a new lockscreen with notifications - and only notifications, not like live widgets with sweet, sweet info.