I think it's supposed to be ephemeral (not spontaneous). The ephemerality doesn't change with this update as the conversations disappear when they're completed

I think it's supposed to be ephemeral (not spontaneous). The ephemerality doesn't change with this update as the conversations disappear when they're completed (with the option to save important messages). Similar to conversations IRL I guess. You speak with someone, note down/save important things such as addresses and then everything else is lost.