the problem occurs when most of the content comes from Meta (they will likely have the vast majority of Fediverse users). especially if major communities exist on their instance. when meta decides to no longer support fedi integration, those in the fedi are forced to decide between staying with their communities by ditching the fedi and moving to threads or having many of their communities ripped away.

meta will do this at some point as a play to draw users to them, but we can decide if we want to be affected when that comes to pass.

Facebook could just create fake users that post ads as content

Not quite what you’re asking for, but during WW2 the US employed Navajo speakers to use their language for certain verbal communications because it was so different from popular languages and hard to decipher. There’s a lot written about them out there. I would also recommend checking out The Code Book by Simon Singh, it’s a great recap of the history of secret codes and breaking them.