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).
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).