These two concerns were always present, long before Apple’s announcement.
Any app that has access to your photos can scan your on-device photos for anything it wants. This could be for benign reasons (e.g. Photos creating “Moments” for you to review) or hostile reasons. Your only safeguard is Apple’ App Store policy.
Apple could always (going all the way back to very first iPhone) design and deploy new software and secretly push it into your phone. There is no technological mechanism that can prevent this short of hacking the phone to permanently disable all capability for software updates. You have always had to trust Apple’s intentions here.
Ditto for all other smart phones. Google, Samsung, Motorola, LG and wireless carriers all push updates into their various phones and devices. When you use them, you have to trust them to not push objectionable software into your phone.
Ditto for your computer. Unless you disconnect from the Internet and refuse all updates, Apple (or Microsoft, or Dell or Google) will push updates for their respective software. Although you can (usually) configure your computer to not automatically install updates, if you don’t trust the company with that ability, then you probably shouldn’t be trusting the disable switch either.
Even if you go open source, you can’t eliminate that problem. Sure, the Linux community audits major packages all the time, but how many normal users actually know anything about the updates that they get from the standard Debian (or Red Hat or Ubuntu or whatever) distribution server? Again, you are trusting your distribution to do what they say they are doing.
In other words, unless you take all your electronics completely off-grid, you are always implicitly trusting someone with matters of privacy and security.
For most of us the answer to “how can I ensure that my system will remain secure and private against direct action from governments” is “forget it, kid”. But it may still be useful to ask the question “who is most likely to give in and who is most likely to resist”, knowing full well that everybody will fold if the pressure gets high enough.