He pointed out that, although such a move could make Apple more efficient as a company, that isn't the firm's focus. "It's about giving people things that they can then use to help them change the world or express their passion or express their creativity".
At the Chicago event, Tim Cook said, "We don't believe in sort of watering down one for the other. So this merger thing that some folks are fixated on, I don't think that's what users want". Again, this is directly contradictory to rumors of anonymous sources spilling the beans on plans to brings iOS apps into a working capacity on macOS through an initiative called 'Project Marzipan'.
However with this code, it seems to hint that Apple could be looking for a way to change the appearance of apps running on macOS globally, meaning that users won't need to be at the mercy of developers for a dark mode which can come in handy in low-light situations where apps with bright/white appearances can be glaring.
Apple has not launched any touchscreen Macs, and while macOS and iOS now share some services and other features (like the APFS file system), they are still very different operating systems for very different use cases. Seeing iOS apps on macOS is a huge leap from iOS and macOS sharing development tools. "So we want to make the best tablet in the world and the best Mac in the world".
The developer community could also benefit by offering its apps to both Mac and iOS users without too much extra work.