It's missing proper support for eGPU cards, which is currently the only way to add a high performance GPU to any currently produced Mac.
Blender, for instance, can't even make use of th GPU in my MacBook Pro because the openCL support in macOS is not good enough.
As a app developer who wanted to build an app which challenged what a mac can do with regards to productivity I had to basically leave the mac app store because they made it impossible for me to make it work in Sandbox mode.
Trying to get modern Unix software to run on OSX is getting more and more painful. Since development is the main activity I do on a laptop, this is quite important.
Apparently as someone that favors Xerox PARC way of thinking, I am not a developer, as I don't embrace the UNIX religion.
You have to admit that around 2003 or so there was a huge influx of technical users to the Mac. My proposition is that a lot of those users were developers moving from Linux (or from an unhappy Windows life, wishing they were using a Unix-based operating system).
I base this on the general sentiment at the time, and I was one of the people who made the switch. I'm sure you can find old posts from me on Slashdot talking about how great the switch was.
Now I'm on Hacker News, talking about doing the exact opposite. I'm moving away from OSX because the Unix experience has become really bad.
Personally I know UNIX since Xenix days, do have a vast experience across UNIX variants, use it in some form in many projects, but rather use OS X and Windows environment.
For strange as it may seem, some of us are actually happier with the GUI developer tooling culture of OS X, Windows, Android, iOS.
What is it missing? It's been a while since I really wanted a feature in the desktop OS. All of the 'phone' features (besides launchpad) have made my life a lot easier (continuity, handoff, notification centre, even Siri from time to time).