For example, there's no reasonable expectation that singing to myself in public won't be recorded.
But almost everyone in public does reasonably-assume that their every step isn't being permanently logged by a stalking drone swarm.
Blending into rush hour foot traffic is easy, and I never feel like I stand out enough to attract attention... though in the back of my head, I know that most commercial and government properties have some form of video surveillance, probably backed by some kind of (hopefully coarse) AI subject tagging.
No opinion on the decision from OP's post, just noting that, privacy is getting 86'd six ways to Sunday. All that's left are truly owned homes and natural spaces, and Orwell laid the pattern for both.
A bit "meta" here, but this was never about surrendering to advancing capability, humans have been capable of eavesdropping ever since eaves were invented, people could bring hidden microphones and cameras in "private" spaces for decades, etc.
The "reasonable expectation" doesn't come from our fears of the worst, or else it would be meaninglessly permissive. Rather, it's an attempt to judge individual situations based on some kind of collective agreement about normality. Just because we can't preemptively block something doesn't mean it cannot be a crime.
In other words, we (should) have a lot more power to decide what they become than that. Supposing--and I'm not endorsing this--anyone caught recording in public typically gets their stuff smashed by an angry mob, then the "reasonable expectation" is that you're not being recorded.