I heard the book has a cheesy ending while the original SCP version leaves it open.

My opinion is that SCP-3125 is something like game theory, or death anxiety, or knowing the most effective way to make money (which is applied game theory), that if everyone thinks about it too much, destroys the world.

These are your type 4 antimemes. Death anxiety leads to the rational conclusion that nothing is worth doing so you might as well just die immediately, and this takes the idea with it. (Healthy humans have developed irrational ways to suppress this.) (Particularly unhealthy humans might also realize that society and the human race don't matter, or that other humans existing are suffering for no benefit.) Perfect knowledge of game theory leads to a cut-throat world where not much survives, again taking most of the idea with it, as well as every idea that's not part of the optimal winning strategy.

The book is better conceptually than history wise.

Interesting your type 4 final stage nihilism, not sure if it will consider a type 4 given that it only self destructive.