What do you mean? How do you expect the author to "make search powerful"? This system is clearly in the context of a desktop/NAS filesystem, so they're stuck with whatever search systems exist. I honestly don't plan to use this system, and still feel the need to respond to this critique of it.
> Why use numbers?
Is answered here[0], to intentionally preserve ordering. You don't need to know what a plain ID means, because the only reason to use it is in context.
> What if categories do overlap?
There's nothing to stop you from tagging things in addition to using this system, if you want.
> dismisses search without giving any reason
Again, the author is not building their own document storage system.
> Additional metadata
This system is trying to solve the problem of having to supply a bunch of information to find a specific document.
Overall, there are lots of anecdotes here about how this system is useful in some situations. There's really no reason to sound so incredulous about it, even if it's not for you.