I readily admit I have not read the book and so to try to critique it in any way or discuss it on any intellectual level would be grossly unfair. That being said, however, you point to the Millennials as aged 5-26 currently and state they are united. I agree in theory they are not or won't be divided along racial or gender lines and a little less so along idealogical lines but what points to them being united along any line as the younger ones are still in the world of the world revolves around me. Plus- there will be the usual divisions along socioeconomic and societal inequities that plague and divide the other generations and are the forefront of the presidential race today.
I do not think based on the age bracket or the current state of affairs that 9/11 or the Iraq war will be the unifying event. Those 18-26 year olds fighting in Iraq and Afghanistan will be as out of touch with same age and the younger Millennial's as the Vietnam veterans were/are with same age and younger boomers who have not been affected/nor understand and won't qualify as any uniting event among the 5-26 year old generation. I think the 'event' has not happened yet but see much potential in the next 4 years for something far greater that affects more of that generation and has more of a lasting impact and impression on them. (sad to say)
As I said I haven't read the book and sure the 'research' is sound but looking at it simplistically based on generational age and data I don't think 2008 is going to usher in any long lasting makeover at least not based on 9/11 or the two current wars. The economic issues may announce the beginning and building beyond but only if solutions are being seen and felt between 2008-2012. We haven't bottomed out yet and hopefully we raise our bottom before we do.