Discussion
This is not a subkey proposal.
He is talking about the problems of it
What nostr:npub1cgd35mxmy37vhkfcmjckk9dylguz6q8l67cj6h9m45tj5rx569cql9kfex meant is that he is not proposing that Nostr users have subkeys for themselves, just encryption keys that they use to encrypt messages in a group. The goals are very different and in this case it doesn't pose any problems to the protocol.
There are always going to be tradeoffs, I can easily see a shared key shared through gift wrap DMs be a good enough usecase for something like say: regular "Instagram stories", it is good enough privacy of content.
Privacy of metadata is also very hard to crack I. This case, but still maybe doable with chain analysis kind of stuff.
So.. Should you sell drugs with this something like this? Probably not, could you share fun food pics on your stories with your friends that you don't want to tell the whole world about?
Yes.
Idk I think key rotation or encryption key is over complicate something we don't need nip17 dont leak metadata, unless you are supposing people will lose the nsec and all their history gets compromised or something.