Sad to say a few people have already set themselves on fire over this and it was quickly glossed over and forgotten, so even your extreme example isn’t guaranteed to do anything.
You’ve had a couple good replies that answer your question, just thought this was worth pointing out.
That’s exactly what the GSMA is saying. Universal interoperability means not having to use Google’s encryption method, therefore iPhones and all other phones including customized Roms should work.
Now, they could absolutely get in the way of this, but I would hope that they would think it’s not worth the effort.