A revamped notification system will be on iPhone OS 5. Why? Just look at the pattern: (The following statements are just my general observations of peoples reactions to the various apple announcements)
2007: iPhone announced, everyone is amazed, they call it the jesus phone, but as the hype dies people start complaining about the fact that it doesn't have 3G or GPS
2008: iPhone 3G: Yay it's just what everyone wanted, it finally has 3G and GPS, oh and look! Now we have apps... But why doesn't it have copy and paste? or MMS, or a Video camera? every other phone on the market does why is apple not listening to their customers...
2009: OMG copy and paste! Look and now we have MMS and tethering too (For non US), and there is that video camera it needed to be a "modern" phone, plus now we have push notifications that will be just as good as multitasking... Or not, how could Apple not have realized we needed to listen to our streaming radio while surfing the web, who cares about how it will effect battery-life I want my true multitasking!
2010: Multitasking! and Folders! and more awesomeness, but look at this, how could apple have not revamped the notification system, its obvious that its annoying, how could they not see their customers need a streamlined notification system, what are they thinking...
Honestly I get it, some of these things should of been thought of, they probably were, there are probably prototypes of every feature everyone ever wanted in the Apple campus, but Apple can't read our minds, they put their focus and development behind the features that seem to get the most reaction from their customers, and that they believe are the most important, every time they release one we have another thing to complain about. Along these lines, this is why I suspect that the iPhone HD will have a front facing camera (Because thats all people have been talking about since the 3GS, and actually since the 3.0 announcement, kinda like these notifications).