These things take time. Remember that blue screen when they announced USB plug and play support in Windows 98?
USB-3 controllers won't initialize reliably if there's a single low speed device conntected, like e.g. the keyboard/mouse I've connected to the USB-3 hub my my monitor, which I'd like to connected to a USB-3 port of my computer so that I can plug thumb drives into the side ports of the monitor.
If the do initialize they take ages to go through POST.
After waking from S3 it takes several minutes(!) for all devices to come up properly. Often the OS drops the controller into USB-2 mode, because keeping it USB-3 creates interrupt storms or similar.
Just having enabled the on-board USB-3 support without anything connected may cause random POST hangs.
All of this happening on pretty recent hardware (late 2015, but still available for purchase in that configuration as of today) with latest BIOS and drivers.
And that's without the issues USB-C introduces (alternate modes, power delivery, which requires driver support, etc.).
I wasn't sure if this was an issue with KVM, USB-3 or just a general issue with nesting hubs (even though I'm running low speed/power devices and a 3.1 port should be able to handle it) but you make it sound like it might indeed be an issue with USB-3
I just want to say that Windows 10 does feel like Windows Millenium (an 'incomplete' OS).
Windows 10 is very well polished. It's also the first windows where most of the user's gripes are stuff added on top of it (telemetry, simplified/restricted update system, ...).
Windows ME, by comparison, was so bad that merely leaving it running would end up causing PC Health crashes.
Well, aside from Windows Defender steadfastly turning itself off because it thinks I have a different AV package installed (I don't) and "helpfully" redirecting me to uninstall the offending software first. Only there is no other AV package to uninstall.
I have so far been absolutely unable to find any sort of resolution to this issue, short of a full reinstall.
But the kernel and system side are miles above ME. We're talking about a time when you could turn a system on, sit there and watch it for a couple hours without touching anything, and it would crash itself.