A big thing to understand is that the jailbreaks have also become "more complex to use and maintain for the user" in addition to "less likely to be found" for the developers: the jailbreaks available for iOS 9.3 and later versions are brutal... they take the form of an app that you had to install using a tool I wrote called Cydia Impactor, which pretends to be Xcode and do all of the signing for a "free developer account". Every time you reboot your device, it is no longer jailbroken, and you have to run this app, which sometimes doesn't work (on iOS 10 I'd even say it "only" sometimes works ;P); and the app itself expires every 7 days (Apple restriction on free developer accounts), and so you have to keep reinstalling it using Impactor. Finally, if you break anything at all that causes SpringBoard to not be able to pop up (as you need to get all the way to "I can see this app and click it" for the jailbreak to work), you have to format your device (losing all your data) and restore to fix it... older jailbreaks were much more forgiving, as you could still log in via SSH if the device even sort of was able to start.
I'll also say that the general issue you bring up was also true for iOS 7 and 8, but there were tons of people who jailbroke even with iOS 9. When jailbreaks are available and easy to use, developers do cool things that are able to tempt users to do it; it is like: why does anyone install an app when I bet they don't really need it? Well, spending $3 for some random app that only slightly affects what you do is worth it: the cost is low to match the low benefit; so it doesn't really matter that much if the benefit isn't "insane killer thing that everyone has to do or the phone is worthless": it only has to be greater than the cost, and the cost went up so high and so fast during the past year and a half that even I have been "living without" a feature I used every single day numerous times and am constantly sad to not have right now, because "damn it, I just don't want to have to spend ten minutes rebooting my phone over and over again in the hope that this broken jailbreak works".
In the last year or so I wanted to take an old iPhone 5s, a handmedown from a relative, to learn CyScript and the other one from the NowSecure engineer that exposes a JS interface (I forget).
How can and how will security students learn to reverse engineer at runtime and assess modern iOS apps in the current state and no official emulator to boot?
Unlikely. The demand for pirated material (games) has not diminished. Also its hard to explain why the iPhone suddenly lacks demand for jailbreak when the Android modding community still thrives.
>These days, I think most users are generally happy with the status quo
Jailbreaking was not a thing for most users.
Your point still stands of course: Jailbreak is not at all needed for privacy.
I personally have held my iPad back on iOS 9 for the reason that maybe some day I could jailbreak and install another OS, home brew apps etc. but I made a generalization about piracy I guess because I did see a bunch of demand for that in 2010-2012 which shows you how out of date my iOS knowledge is (since I have not jailbroken any devices between then and now). By the way, thanks for Cydia :) its synonymous in my mind for any discussion about jailbreaking and iOS.
I just think there is some demand for jailbreaking, and lack of public demand isn't a significant explanation for lack of jailbreaking progress on iOS 10/11. I mean, there is no clear argument I've seen yet which establishes a link between public demand and frequency of jailbreaks; after all it only takes a single determined developer/hacker to craft an exploit and deploy it for reasons not connected to public demand.
For the most part, I agree with this, and I was making this argument somewhere else in this thread: the primary reasons that we haven't seen many or, when they happen, "pleasant" jailbreaks for recent versions of iOS is that Apple has continued to be good about not having severe regressions in their attempts to secure the device, they have added really interesting mitigations ahead of the competition, they have changed their prioritization for plugging holes (they used to let jailbreaks sit around for months), and they've hired many of the more "mercenary" people who would work on jailbreaks away from The Resistance to work for The Empire.
That said, there is at least some connection with demand, and that's something worth examining in more detail here.
> ...after all it only takes a single determined developer/hacker to craft an exploit and deploy it for reasons not connected to public demand...
The way you word this sentence makes it sound like the work involved here is comparable--not just in quantity but in concept--to building a real-time chat application or some other slightly-complex web application. This isn't just "work": it is a combination of luck and skill that relies on winning a game that you are playing against an opponent (Apple) who had to make a mistake; if anything, it has more in common with panning for gold than building a bridge. One does not just "craft an exploit", no matter how determined.
The reason people are willing to burn tons of time into the possibility of finding a vulnerability in this platform is because there's a ton of PR and excitement to come from it, which is largely tied to the amount of interest that exists. There are tons of less secure devices out there that never get anyone bothering to "jailbreak" them due to lack of interest; people even take up bounties to try to get these devices hacked. This is made much worse as there really aren't that many people who can even pull this off when given an end-to-end explanation of a vulnerability.
What ends up happening, thereby, when there isn't much of a public interest in jailbreaking, is that these people spend their time working on hacking other devices or they hoard their exploits (as why bother burning your magic trick on people who don't even care for the performance?), whether for personal use (it makes a great parlor trick while also letting you do a lot of great research into the workings of Apple's software) or to sell for a profit (which might be to Apple through their bug bounty program or to a third party; the latter brings up interesting ethical questions, but people definitely do it: these exploits are then used either to do more research or are turned into weapons).
We can then ask "why has demand in jailbreaking decreased? as in, why does this matter?", and I see a few reasons: one is that Apple has started "throwing in the kitchen sink" (seemingly after waiting for Steve Jobs' body to be cold in the ground...), another is that the extremely killer and pressing needs have started to go away as Apple fleshes out the operating system as well as allows more things into their App Store, and another big one is a kind of "death spiral" that comes from there being less to do, leading to fewer people bothering to do it, leading to less reason for developers to develop cool stuff, which is why there's less to do... this collapsing market is a really tough sell.