For how much longer? I'm not asking facetiously, the trends across the entire industry are quite obvious at this point. [...] I'm sure there are no ulterior motives at play here though. /sIf that's Apple's trajectory, why did they things like Hypervisor.framework (much more recent than 10.6's introduction of the App Store), which allows one to make unprivileged virtualization solutions, that can run any OS/application?
To me, it their motivation seems two-fold: (1) they want to carve out a niche for security and privacy. People are willing to spend a lot of money to avoid the data grab of Facebook, Google et al. And people are willing to spend money on a system that focuses on security. So, Apple have invested a lot in hardware security (T2) and software security (sandboxing, read-only system files, mandatory kext signing, user-space drivers).
And, yes (2) they probably also want to funnel more and more through the Mac App store for profit. The thing is, they can make macOS a walled garden system, while keeping the back door open for advanced users. My dad is protected by the Mac App store, application bundle signing, notarization, and sandboxing, he is not going to boot in recovery mode and run csrutil in the command-line. While I can in the use csrutil to lower protection a bit to be able to run DTrace. In other words, I don't believe that they want to or need to turn macOS in a complete walled garden: 90% of the users does not want to or cannot disable security measures, while at the same time keeping the csrutil around keeps the other 10% happy.
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I think the more serious danger for macOS was negligence. With key execs primarily using iPads and glacial development of macOS, the most imminent danger seemed to be that macOS developed into nothing else but an SDK/IDE for iOS development. But after the last WWDC, I am mildly optimistic that they have woken up.