Some remarks on that from their CTO and engineering lead: 

"there are multiple longterm options being discussed for plc, but the most well-regarded right now is an neutral ICANN-style org to operate it"

"Technically, Bluesky PBC is still operating the PLC directory (we are actively exploring how to change this). However, there are already independent developers in the ecosystem who are mirroring and auditing the stream of operations from the directory, so any retroactive manipulation would be observed and called out."

That debate aside, nostr is quite magical for the sheer lightness of it all, it's like travelling with only a carry-on and priority boarding all the time, I can't see any other architecture coming close there.