He can't really really announce the split timeline in-game because the inhabitants of Hyrule aren't aware of it.
I didn't mean that. I meant their weren't any obvious factors that indicated that TP had to be on the child timeline. Super Ganny's point he questioned about me in my "Whereabouts of the Timeline" article are proof of that. If I were a Splittist then before the confirmation, the only lead way I had was to argue that Ganondorf was not in the Sacred Realm as he should have been had the timeline been linear. But as the fierce Linearist I was, my arguements can be parallel with points that Super Ganny made before in regards to "legendary hero" being quoted throughout the game, weapons like the bow and tunic being recovered, and such things like Ganondorf still having the Triforce of Power, hyroglyphics of images in Archibalds Grounds that looked like Ganon depictions, ect... Point is that we did not have any clear indication until Aonuma said something. And when we did, then Splittists could rule out the Linear Timeline in full, like how I demonstrated with Super Ganny.
The producers could make fixing the timeline so much easier if they wern't afraid to release one already, but they don't want to restrict themselves to it at the same time. But alls they have to do is make simple undeniable references from one game to the other where we can clearly point out that theirs no arguement to whatever the canon may be.
It's possible that some day a game will be made in which the plot will revolve around the 2 Hyrule timelines, especially if someone like the Happy Mask Salesman (who is known to travel between different worlds) discovers a way to travel between them. Termina might be a link between the two Hyrules, even if the "doorway of time" is closed. Or the game could revolve around the Goddesses wanting to "fix" the split timeline into a single one again. And these are just 2 very obvious ideas from someone who is only a fan. The game designers themselves are known to come up with some very crazy ideas from time to time, so who knows what future games will involve.
Don't count on it unless we do something about....
http://hylia.ytmnd.com/
