Touch screen computers are great for casual use. Such as at a kiosk, or on an iPad that you use to check email and read the morning news.
However as soon as you want to do something more intensive, such as composing a long email for business recipients, or content creation. You are going to want a laptop or desktop with an actual keyboard and keyboard shortcuts.
The keyboard and mouse may seem stodgy and outdated compared to the far out high tech of touch screen technology. But from an ergonomic standpoint, touchscreen is a a torture chamber. If you are working 30–40 hours a week on a touch screen with no mousing device, you will develop ergonomic issues. The angle at which your arms interact with the device is less relaxed. You have to lift your whole arm and point, drag etc. As opposed to mousing with a relaxed arm which is only minimally deflected from a resting state.
Speaking of deflected, this is one of the main issues with touch screen interaction. Imagine that you are sitting in front of a screen at a desk. Draw a line through the middle of your head down through your body, perpendicular to the floor. This is your centerline. Using a mouse or trackball causes minor deflection from the centerline. Using a touch screen creates major deflection. It’s not of concern in casual use, but over the course of the work week it would begin to contribute to musculo-skeletal problems.
Of course one could change the angle of the touch screen to be less vertical, maybe a 45° angle could be more ergonomic for touch interaction. However, this will put one’s neck at a bad angle for long term use.
At it’s core, the IOS platform is about entertainment. Passive consumption of content as a liesure device. IOS does not have a filesystem, or a CLI or robust multiuser login.
At it’s core MacOS is a workstation platform. It excels at content creation, business administration and other repetitive tasks which benefit from a fairly bland, uncluttered UI.
If we are to judge by WIndows recent iterations, bringing the mobile environment to the desktop involves scaling up of icons and reduction of user access to system settings.
Now of course, we can package binaries with different sized assets to be deployed for different environments, desktop, tablet, smartphone.
We could also code all of the behaviors to work in a touch context or click context. In fact we already do this for responsive websites.
However, it is hard not to imagine a merger which negatively affects the user experience of the desktop user, for the benefit of the mobile user. Look at the sales figures at Apple. Laptop and Desktop trail far behind mobile.
Merging a mobile OS and Desktop OS you end up with something which is good at neither. A Chevy El Camino. Not really a car, but not enough of a truck.