I am not saying that's easy but unifying development for desktop and mobile seems harder. I think a lot of people have concluded that it's pretty much impossible because the needs are too different.

For developers this transition was quite seamless, since most of the high-level API functionality was still there. This isn't the case when you're ripping out the current UI framework that every app uses.

That was over ten years ago. The Apple of 2017 is a totally different company, and I don't think they're capable of pulling this off.