[shadowfiend]

There is no iMessage app. There is a Messages app that implements two systems: iMessage and SMS/MMS. iMessage is the system whose security model is being discussed here, and the security model of SMS/MMS is mostly irrelevant to it.

[danShumway]

This is splitting straws; the overwhelming majority of Apple users don't make this distinction (if they even realize there is a distinction to make). For all practical purposes they use one app that lets them talk to their friends and some of the bubbles are green and some are blue. How many of those Apple users even realize that the green bubbles are unencrypted rather than just being a designation for Android contacts?

It also changes nothing about my comment, because you can call SMS a different system all you want, but your conversations with Android users are still being sent unencrypted and any malicious payloads you get from SMS phones are still being loaded into the same Messages app. If you're worried that a 3rd-party client on Android is going to let a company spy on conversations you're having with Android users, then I still have real bad news for you about how Apple sends messages to Android users.

Draw the lines however you want between Messages and iMessages, but the security implications of Apple's setup are exactly the same. When you write a message to an Android contact, Apple sends that message unencrypted to a 3rd-party client that could by spying on you, leaking your data, or sending malicious payloads to your iOS Messages app. It still makes no sense whatsoever to be this concerned about the security of the push notifications for your messages to Android users when the alternative being proposed is to throw security entirely out of the window for those conversations. It is still a clear security improvement for conversations between Apple and Android users to be E2EE rather than to be sent over SMS, because the risks being raised about 3rd-party messaging clients are already present within those conversations today.