But iMessage is synced between devices. So if I delay a send on my iPhone and lose network, my other Apple devices know enough they could still send it.
Should they (I asked to send) or not (‘sending’ device offline)?
If it's E2EE, why not send the message with a timestamp at which the server should approximately process the message? If it's well encapsulated/encrypted, it shouldn't matter that the message is on the server for a while.