Gregory's ServerThis, from "Federation Architecture Overview," is also pretty wild: "For example, the BGS might crawl to grab data such as a certain post’s likes and reposts, and the app view will output the count of those metrics."
#Bluesky's solution to the out-of-sync metrics people sometimes complain about on #Mastodon is to separately crawl for likes and reposts, and pass that info through the App View. Which seems like an opportunity to inject false metrics, particularly if anyone can run an App View.
The post says that #Bluesky is experimenting with breaking Labeling and Feed Gen out from App View, so this more complicated infrastructure isn't necessarily the form the network will ultimately take. Hopefully, they'll walk back that plan, because it seems to me that the flexibility it adds mostly opens up new vectors for bad actors who want to reshape traffic on the network to their own ends.