Definitely not gonna be like what happened with Windows Metro apps
Bizarre doublespeak in the presentation though as they denied this was the plan - explicitly said no merger.
"Are you merging iOS and macOS?" "No."
Then proceeded to detail the port of the iOS APIs to Mac and some apps just using those APIs.
Time will tell, but I think a merge is exactly what they are planning long term, and it makes sense to do so (with some differences for user input and larger screens). It's crazy to develop very similar APIs for GUI apps in parallel, and what has become two different OSs with slightly different apps and feature sets, but a huge amount of overlap. The savings for Apple and developers of having a consistent set of new APIs and one set of apps to manage (for example their entire office suite) would be huge.
The sheer pressure of money and users on the iOS side means that will be the dominant one, and UIKit will win.
Re lockdown, that's more a political decision than a technical one, it could go either way, I suspect both platforms will become gradually more and more similar (they already are converging) and the future will be close to the one you fear, with at the very least some ARM powered locked down laptops (which I'd be very happy with).
Right, and what the announcement seems to show is that UIKit could eventually grow to replace AppKit. Like you yourself say - "uikit is a better appkit written with the benefit of experience".
That still doesn't imply the two OS would necessarily be merged - there's still a ton of things that make sense for macOS that are not needed in iOS, and vice versa - just for one thing, they have vastly different energy budgets. There's also a ton of overlap and shared code already, for pieces that it does make sense to share.
So, I still think the answer is really targeted at people who fear that iOS (with all of its current limitations) will replace macOS, essentially, rather than being a misdirection as you seem to find it?
From a developer perspective, I expect them to arrive at one API, with a few options to allow feedback from various sources (tap or click), and handling multiple screen sizes gracefully, and therefore pretty much one OS, so that you can build one app across devices - this is exactly what they are trying out with their ios app port. Once you do that, it doesn't make sense to have two APIs.
I can't think of many features that would be exclusive - to take your example of energy budgets, saving energy on both is equally important now that laptops are a mainstay and desktops an afterthought. We may well see ARM laptops for this reason. Watches are the one exception that have a budget so tight at present that normal apps just aren't feasible.
So I think a merge is exactly what is on the cards in the long term, particularly as they are now run by an operations person and the money flows in more and more from phones, not computers.