You know the more I think about it the more likely this seems.
We're the ones on the side of the wall that created all these fictions in the first place. Their unvierse exist
because of our interference. It seems less likely, therefore, that any of them could have broken the wall from the inside, at least not without help from outside.
Fictions CAN'T manipulate reality. But we've been rewriting and manipualting
them for centuries. We've been breaking fiction down in our heads for years. We've gotten to the point where people from reality are engaging directly with ficitonal characters (TV series based on people, online webseries where people play as characters, but are quite clearly being themselves, this very ARG, etc...)
Hell, maybe the wall breaking down just... started happening. We aren't strictly to blame, even if our actions caused it because we didn't know we were doing it. Remember the Therapist's early post on... what was it called again? Cooperative therapy, or something like that? Sorry I forget. But I remember her theory just about.
I'm not sure how to explain this, but I'll try

: Ever since the creation of the internet the way we act and think about both reality and fiction, has completely changed. We are creating stories and forging cooperative efforts that as little as fifteen years ago, wouldn't have been possible. The pace of living too, has sped up by about a hundred -stories aren't limited to slow word of mouth or publishing in books and magazines: they can be thrown into the world extremely quickly via online blogs, writing websites, hell even fanfiction. Can you see people posting fifty odd pages worth of chatter on Sherlock Holmes a hundred years ago? Maybe, maybe not. But if they'd HAD the internet back then, they probably would've... the only thing we were limtied by was our physical capability. And we don't have that limit anymore. How we tell stories has changed.
My point is, maybe us doing all this work on a meta level has begun to have an impact on the physical? You've got all these ficitonal characters who have been talked about for years, and have seeped into popular consciousness... Mix it all together and what you've got is a seriously powerful sense of being.
The Fourth wall is the thing that protects fiction from reality (and perhaps vice versa), but maybe we created it, sunconsciously, to protect us from the confusion that results when reality and fiction merge. We NEED to be able to differentiate from reality and fiction or else... well, we go crazy, like Don Quixote.
Maybe at some point the Forth Wall WAS just an idea,a concept, but like how in Terry Pratchett novels beleiving in gods gives those gods power, us going on and on about the fourth wall for all these years amde it something tangible, something would COULD be physically shattered.
If that made any sense I will be very surprised...
Edited to add: sorry, wall of text.