I heard/saw quite a few people saying Apple either couldn't or wouldn't cut them off—and that even if they did, it would take a while. They were ridiculous takes, yes, but apparently made in earnest.

While it would ruin the experience in practice (not being able to receive any notifications), I don't see why someone couldn't perfectly reverse engineer the protocol.

Beeper made several design decisions that made the app super easy to use (i.e. using a single certificate that wasn't supplied by a user's phone), but if you extract the necessary source material from an old jailbroken iDevice, you could create an iMessage clone that Apple can't ban without either legal action or breaking compatibility with all easily jailbroken iOS devices.

Back in the days of AIM and MSN, even large companies used reverse engineering to get chat interoperability, and it was so successful that AIM left open an RCE vulnerability to push shellcode so that Microsoft couldn't chat through their service.

Any source/articles about the AIM RCE and it being left open? Would love to read about that

Here's a long writeup by someone who worked at Microsoft at the time: https://www.nplusonemag.com/issue-19/essays/chat-wars/

The "well duh" crowd says "well duh" no matter what happens.

Mmm, absolutes.

There were a lot! Usually taking the form of: 1. They’ll have to do a major update to iMessage, 2. But what about Hackintosh?, or 3. EU regulators will stop it

A good chunk of the posters on the release thread seemed to think otherwise.