I don't think that is coming. The fact that it took so many years to add some "desktop os" features to iOS shows, that they try to keep those branches separate from the UI model. From the underlying OS technologies, they are very close together. E.g. APFS, while introduced on iOS is coming to macOS with High Sierra.
So for the next years, I would expect iOS and macOS to share, what makes sense, but keep the UI separate, where it matters (touch/pen vs mouse/keyboard).
I don't see why/how – they are _completely_ different UI interaction models. Superficially it looks similar, but the one thing that really set iOS apart, was to build UI concepts that targeted finger interaction first (UINavigationController and UITableView are stroke of genius).
Everything from how big the area for a tap is, to how to work with highlights, how dragging work, how things are aligned, what deliberate limitation etc, are different between macOS and iOS.
I hope so. I feel like this has been Apple's end game for quite while but they have been squeezing out the profit from the movement towards that in the interim. I mean, the new Macbook ribbon thing, what a piece of crap compared to the innovation of a Surface Pro.
But if you can give me a Macbook's power with a touchscreen and detachable keyboard - "Here, take my money!" :)
They are certainly experimenting with which features might make sense on the "other" OS. But until your post, I had almost forgotten that the launcher still exists on macOS. Likewise, Dashboard still exists, but does not get much attention any more. But even with the new iOS giving more "desktop" powers to the iPad, Apple still seems to aim for a UI model quite different to macOS. So this seems to be intended.
That launcher may be indication Apple was thinking that way, but look at their latest U-turns on pro hardware and reinforcing their commitment to laptop/desktop. I don't believe they're going that way anymore.
Also. Did you ever see anyone using that launcher as primary interaction?
