
Chunky buttons.
For me, the big takeaway from the Microsoft Edge web browser in Windows 10 is the chunky sparse interface.
I love it - and I’m not using touch.
In addition to making it touch friendly, perhaps surprisingly they also make it nicer to use with a non touchscreen. Bigger touch targets force the app to have an uncluttered interface with fewer buttons - and make those it has very easy to hit with minimal mouse precision.
So, even if touch isn’t ever coming to the Mac - big buttons are much nicer and easier for users - this is my Dock right now in OS X:

and I love it vs my older more cluttered dock.
It lets me focus on what I’m working on and click targets are much bigger.
Bigger click targets require the user to think less and not be as precise - which help to get the OS out of the way and make using it less stressful and more fun.
The first thing Apple could improve, and the most fiddly aspect of OS X at present, is the red, yellow and greed buttons in every window:

These could be made larger right now - with very little effort. You wouldn’t even have to make the surrounding bar larger.
There are also positive accessibility benefits here too for those with sight and motor impairment. (I often find improving accessibility improves an OS for all users - not only those with a disability).
I hope we see this in OS X Weedpatch.