Partial answer here: https://blueskyweb.xyz/blog/5-5-2023-federation-architecture
"The federation architecture allows anyone to host a BGS, though it's a fairly resource-demanding service."
BGS = Big Graph Service, #Bluesky's new jargon for network-crawling data indexers.
This is pretty much the answer I expected: No real guardrails on who gets to index the network and provide feeds. State actors aren't likely to be daunted by the resource demands.
That blog post also outlines a piece that wasn't obvious to me from the protocol spec: "An App View is the piece that actually assembles your feed and all the other data you see in the app, and is generally expected to be downstream from a BGS’s firehose of data."
So algorithmic filtering presumably happens on a smaller server independent of both the BGS and PDS, which makes the #Bluesky nerwork even more complex than I visualized in the OP. And presumably, anyone can run an App View, too.