The "It's Been Way Too Long" tagline is still very curious to me. It suggests an admission that something on Apple's part is overdue. I really don't think this has anything to do with product lines, as there are no Apple products which are horribly out-of-date, certainly not even to the level of the old Mac Pro, unless you want to count the Cinema Display. But it seems unlikely they'd brand an event just for a monitor.
So I think they are alluding to something more fundamental to the company. What this is, that's the real curious part. Cook has always been more nostalgic for past Apple than Jobs was. When he first started making public comments after becoming full CEO, he called Macs by their old name, "Macintosh" a few times. Then we got that big retrospective site last year. More recently, they used the old rainbow logo in one of their commercials.
So whether he just has nostalgia, he thinks that tapping into Apple's history has brand power, or both, I think this event is going to be used in part to change something on a higher level about Apple. Perhaps Apple will start using the old rainbow logo on Macs again. Perhaps in their recent interest in fashion, they will start offering some Macs in trendy colors again. Perhaps they will announce that they'll be manufacturing Macs in America again. Whatever it is, I think it's a tie to Apple's past and Apple's future.