And they'll continue to say that right until the moment they yank the rug out from under you when all the pieces are in place.

The trop that your logic falls into is there's no way to disprove Apple will ever do this.

10 years from now, we'll probably be having the same argument, and people will be pointing to the latest release of macOS and complaining that surely this one means the end is nigh.

Indeed. I've been hearing people crow on about this since Lion. That was 10 years ago. OS X might be macOS now, but it's still fundamentally the same OS.

But there is an easy way to prove that they will and that 10 year horizon is short enough that I believe it will happen. Apple never cared about developers, they care about moving units and profits. Right now they are not getting a slice of the action of all software sales for the Mac and that must be a temptation they find hard to resist.

Remember how they turned their backs on the creative people that kept them alive for over a decade when everybody else had switched to windows? Similar story, similar ending.