"Rotation doesn’t require abandoning an audience because it doesn’t change the identity people follow." Again, that is true, so long as the client the followers are using has adopted lineage. If it has not, then they will only be seeing the old posts that were signed with the root key, and they will only see the notes from the new derived key if they actively follow the derived key's npub, unless they happen to stumble upon those notes naturally via others they follow who have shared them, or by browsing relay global feeds. Even in the latter case, though, unless their client supports lineage, they would not know that these notes were posted by the same person they already follow, because their client would not be associating them with that root pubkey, it would just appear to be an npub with no profile metadata who posted the note. Is that correct? If so, then adopting this derivation scheme effectively abandons all followers who aren't using a client that has adopted it, making it next to useless unless and until virtually all clients have adopted it, unless the user is ok with the tradeoff of a large number of their followers no longer seeing their posts. This makes it very different from the other features you mentioned that have gained gradual adoption in the past. NIP-05, DMs, zap receipts, and badges all had benefit immediately, even if only one client adopted them, and so users were happy to try them out, and then pester the devs of their favorite clients to implement them, when they saw the benefit for themselves. Lineage, on the other hand, doesn't seem to be beneficial to most users unless and until the majority of clients support it. Until then, it is a detriment to them to start posting from a derived key when most of their followers are using clients that don't support lineage, since those followers would not see their notes. If they want to use it without these drawbacks, they will have to wait until "after the ecosystem you care about supports it, so existing followers aren’t affected." The ecosystem we are talking about here is the entirety of Nostr clients, or at least the most popular ones.