I'm aware of all this, it's the same in sailing and it's a mess. But since aircraft are already set up to use magnetic north, and are basically flying computers

I'm aware of all this, it's the same in sailing and it's a mess. But since aircraft are already set up to use magnetic north, and are basically flying computers, it shouldn't matter what crazy navigation scheme they are using. But a sibling comment already pointed out, what you also mention, that it also affects physical markings etc, and that makes much more sense.