My personal theory regarding Final Crisis is that it will be the final gasp of "Clutter Earth".
As the Multiverse stands now, certain heroes are on different Earths. For example, the Marvel Family is on Earth 5, the JSA is on Earth 2, etc.
Ok, granted there are probably 40 different Supermen (or more) in this Multiverse, but do we really need two Marvel Families and Two JSA'a? I think when the smoke clears, Clutter Earth will be gone. Earth 1 will be the home of the Justice League, Earth 2 of the JSA, etc.
I've been thinking along the same lines... I think it's time to kill off the Unified Earth JSA completely (well, the members that have been around since WWII era)... hopefully the Earth 2 JSA will have a nebulous date in the past when they started (30 years ago)... the Earth-5 Marvels could start now and scrap all previous continuity for new DC Earth... start fresh (meaning don't try to tie in all previous continuity as if it all happened on this Earth)