There were two obvious problems with the way oWoD handled metaplot:
1) The relentless progression of time. Say it is January 2005, and a book has just been released that happens to mention some particularly interesting thing about Detroit in Werewolf, some novel sept structure or something. It catches your interest. You know that in June 2005, Rage Across Detroit is due out. Now you're looking forward to it.
But wait! In APRIL 2005, some other book has a big vampire rampage across Detroit and devastate the local werewolf population. June 2005 rolls around and sure enough, it's about post-rampage Detroit. Whatever you were looking forward to is gone, and will never receive coverage, because the oWoD metaplot progressed relentlessly forward.
2) Written like a serial. The oWoD metaplot was written like a dramatic arcâ€”plot twists and unexpected surprises and an attempt to keep people guessing and wanting to buy the next book to see what came next. A CLAN WILL FALL! THE ANCIENTS WILL RISE! Etc. This meant it was hard to incorporate material from it into your games.
Ex3's timeline isn't either of those things. We're not going to say that just because the Mask of Winters conquers the Marukani in RY 773 in a book published in July, from August onward we're never covering the unconquered Marukani again. (Example pulled out of my ass; I know of no plans to write up the Mask's conquest of anyone or anywhere besides Thorns.) The setting is the whole timeline, and we're not devoted to covering it linearly. Nor will it be written to incorporate a lot of SHOCKING TWEESTS. It'll mostly be about portraying the progression of organizational politics over time, so that by example players and STs will have a better idea of how large-scale organizations interact over time. When the PCs start grabbing hold of large-scale organizations, STs will be better able to run the world's reactions.
So I suspect that stuff that WOULD count as a shocking tweest, like an Autochthonian incursion, will mostly be kept out of the timeline. That way STs who want to use it can actually shiock the players with it.
Exalted has so many things to wow you with, we don't need to do it with a shocking and unpredictable metaplot. To the extent that the timeline is meant to excite and impress, we want to excite and impress you with well-thought and useful it is.