Questions:

If the key can be kept cold, does this mean your posts are not signed by your private key? If so, then how can posts be self-authenticating?

If your public key is effectively a permissionless DNS address that can be pointed to your own server, or to another trusted provider's server, and switched at will, is there censorship resistance via redundancy, or is data only stored on one server at a time?

I really do like the semantic social graph idea, but I think the above are two key strengths of Nostr.