Every newspaper and pretty much any other medium over the past century or so. That’s what editors used to do.
Scaling is not the problem - profits scale with the number of users, the cost of moderation would too, in the worst case. The problem is company’s unwillingness to pay anything at all. Their profits didn’t came from offering a good product, but from discovering a new way to offload the costs of their operation while keeping the income. In this case - by pretending to be a part telco, part newspaper (which brings income), but without taking their main responsibilities (which cost money).
Newspaper editors don't have to deal with large scale attempts to publish material as journalists on the newspaper's staff - or insofar as they do have to deal with it they just ignore unsolicited submissions. That's the closest analogy I can see in the newspaper business.
In most newspapers there has been a section for letters to the editor. Those sections are moderated by editors. That is the reference, not some situation of random readers somehow publishing material, by posing as journalists on the newspaper's staff.
An updated version of that is the comments section for online stories.
The article you linked doesn't say how much fb pays for their moderation. It doesn't say how many people are in their "moderation army". Nor does it say anything current. That article was written 8 years ago.
> XCheck isn't really about content moderation, it is about special security for specific people and how that interacts with posting.
According to the description, xcheck is all about content moderation - it chooses when not to moderate content.