Ava, you're the security professional. 

How is it possible you believe a protocol change could retrospectively delete data in an open ecosystem with bad guys already within the walls? 

 > Ava, you're the security professional. 

Oh, no.
Oh, no, oh no, oh no.
Oh no. 

 How do you unsign a note once someone has a copy? 

Isn't it like un-telling a secret. You have to trust the person you told when you tell them that you don't want to tell them anymore and can they please forget.  

 Clipper chips and signed binaries?

In an open protocol, no one can force anyone to "no longer participate in the network". 

 I know transactions can't be deleted from my node. I know torrents can't be taken down no matter how hard you try. I know if you delete a tweet, people screenshot and they find their way onto way back machine.

It's a trade off we made for censorship resistance. If somehow we can control what other people store and serve in their own relays, we are also dead in the water.

So then what?

Open to your suggestions  

 opsec 

 "Greater privacy" is a moving goalpost.

Not even XMR passes unrecorded and un-analysed. It is nearly certain that the first year's worth of transactions has been largely de-anonymised.

XMR transactions are passing only a few bytes of unique information, and the set of participants is very large relative to the small uniqueness of the messages.

This is wildly inapplicable to Nostr.
 

 You just need poisoned relay and client and this is broken. I'm not saying your proposal is impossible, but my mind is stuck on the untelling of a secret example nostr:nprofile1qqs8x9lez0pauuu7sw4jmhr8qz50tjh5t7k95qkx4zrt2hhekl356sgpzamhxue69uhk56t8vauhgmmd9ejxgmnn9ehx2aqpz4mhxue69uhk2er9dchxummnw3ezumrpdejqz9mhwden5te0dehhxarj9enx6apwwa5h5tnzd9aqye5vk4 used. And I can't imagine how to achieve this in a system on every level.  

 nostr:nevent1qqsfe89fc05rfnz7jhth982e6pwsgjx2hm2yfj75cts9yh8700xgdxcpg3mhxw309a3xjarrda5kuu3kv3jn2mrtweurgarswajx67njv3nxgurvvy6hx7tpxfskvamsvdsky6n4wqe8surfx4j82mrzv9jzummwd9hkutczyprqcf0xst760qet2tglytfay2e3wmvh9asdehpjztkceyh0s5r9cqcyqqqqqqg7pfxlv 

 > Ava, you're the security professional. 

Oh, no.
Oh, no, oh no, oh no.
Oh no.