TBH I'm surprised iMessage hasn't been reverse engineered more--it's a very popular app yet it seems like the only thing backing Apple's claim that it's secure and end-to-end encrypted is "trust me"
[0]: https://www.nowsecure.com/blog/2021/01/27/reverse-engineerin...
The only reasonable usecase I can identify are people writing iMessage bots/ spammers but those groups most likely wouldn't want to open-source their stuff.