The US is very openly, publicly moving down the road called The War on Domestic Terrorism, which is where the US military begins targeting, focusing in on the domestic population. The politicians in control right now are very openly stating what their plans are. It's particularly obvious what's about to happen, although it was obvious at least as far back as the Patriot Act. The War on Drugs is coming to an end, so they're inventing a new fake war to replace it, to further their power. The new fake war will result in vast persecution just as the last one did.
You can be certain what Apple's scanning is going to be used for is going to widen over time. That's one of the few obvious certainties with this. These things are a Nixonian wet dream. The next Trump type might not be so politically ineffectual; more likely that person will be part of the system and understand how to abuse & leverage it to their advantage by complying with it rather than threatening its power as an outsider. Trump had that opportunity, to give the system what it wanted, he was too obtuse and rigid, to understand he had to adapt or the machine would grind him up (once he started removing the military aparatus that was surrounding him, like Kelly and Mattis, it was obvious he would never be allowed to win a second term; you can't keep that office while being set against all of the military industrial complex including the intelligence community, it'll trip you up on purpose at every step).
The US keeps getting more authoritarian over time. As the government gets larger and more invasive, reaching ever deeper into our lives, that trend will continue. One of the great, foolish mistakes that people make about the US is thinking it can be soft and cuddly like Finland. Nations and their governments are a product of their culture. So that's not what you're going to get if you make the government in the US omnipotent. You're going to get either violent Latin American Socialism (left becomes dominant) or violent European Fascism (right becomes dominant). There's some kind of absurd thinking that Trump was right-wing, as in anti-government or libertarian; Trump is a proponent of big government, just as Bush was, that's why they had no qualms about spending like crazy (look at the vast expansion of the government under Bush); what they are is the forerunners to fascism (which is part of what their corporatism is), they're right wingers that love big government, a super dangerous cocktail. It facilitates a chain of enabling over decades; they open up pandora boxes and hand power to the next authoritarian. Keep doing that and eventually you're going to get a really bad outcome (Erdogan, Chavez, Putin, etc) and that new leadership will have extraordinary tools of suppression.
Supposed political extremists are more likely to be the real target of what Apple is doing. Just as is the case with social media targeting & censoring those people. The entrenched power base has zero interest in change, you can see that in their reaction to both Trump and Sanders. Their interest is in maintaining their power, what they've built up in the post WW2 era. Trump and Sanders, in their own ways, both threatened what they constructed. Trump's chaos threatened their built-up system, so the globalists in DC are fighting back, they're going to target what they perceive as domestic threats to their system, via their new War on Domestic Terrorism (which will actually be a domestic war on anyone that threatens their agenda). Their goal is to put systems in place to ensure another outsider, anyone outside of their system, can never win the Presidency (they don't care about left/right, that's a delusion for the voting class to concern themselves about; the people that run DC across decades only care if the left/right winner complies with their agenda; that's why the Obamas and Clintons are able to be so friendly with the Bushes (what Bush did during his Presidency, such as Iraq, is dramatically worse than anything Trump did, and yet Bush wasn't impeached, wasn't pursued like Trump was, the people in power - on both sides - widely supported his move on Iraq), they're all part of the same system so they recognize that in eachother, and reject a Trump or Sanders outsider like an immune system rejecting a foreign object).
The persistent operators in DC - those that continue to exist and push agenda regardless of administration hand-offs - don't care about the floated reason for what Apple is doing. They care about their power and nothing else. That's why they always go to the Do It For The Kids reasoning, they're always lying. They use whatever is most likely to get their agenda through. The goal is to always be expanding the amount of power they have (and that includes domestically and globally, it's about them, not the well-being of nations).
We're entering the era where all of these tools of surveillence they've spent the past few decades putting into place, will start to be put into action against domestic targets en masse, where surveillence tilts over to being used for aggressive suppression. That's what Big Tech is giddily assisting with the past few years, the beginning of that switch over process. The domestic population doesn't want the forever war machine (big reasons Trump & Sanders are so popular, is that both ran on platforms opposed to the endless foreign wars); the people that run DC want the forever war machine, it's their machine, they built it. Something is going to give, it's obvious what that's going to be (human liberty at home - so the forever wars, foreign adventurism can continue unopposed).
Systems of power always act to defend and further that power. Historically (history of politics, war, governmental systems) or psychologically (the pathology of power lusting) there isn't anything surprising about any of it, other than perhaps that so many are naive about it. I suspect most of that supposed naivety is actually fear of confrontation though (you see the same thing in the security/privacy conflicts), playing dumb is a common form of self-defense against confrontation. To recognize the growing authoritarianism, requires a potent act of confrontation mentally (and then you either have to put yourself back to sleep (which requires far more effort), or deal with the consequences of that stark reality laid bare).