Intel NUC are weird little devices; for my home file server, which at most ever has one user accessing at a time, I replaced an old PC tower with a NUC and a 5 disk USB3 SATA dock. It works better, has excellent Linux support, and uses less power.
The device is weird because it strikes me as the perfect HTPC, and yet it isn't really marketed as such.
I've bought something like 10 of them (the oldest two are Gigabyte Brix, but I'll count those with them). There are a few home servers, but the main use is as a pool of machines to use for oVirt, Open Stack, Kubernetes and RHEL work. The machines get wiped and repurposed quite a bit.
They're a lot more convenient for this than actual 19" servers, since they take up a tiny fraction of the space and power of even a single server. However they would be so much more useful if I could remote IPMI into them rather than having to find a monitor, keyboard, HDMI cable and mouse every time I want to fix them.
They would also be reasonable for home theatre since they are silent and low power, while at the same time having decent CPUs, but they use Intel graphics so I guess they probably can't drive 4K + 60Hz displays, although I've never actually tried.
I only drive a 1080p display with it, so I couldn't comment on 4k; however, it runs most everything I throw at it from my Steam library, reasonably well. The newer Intel GPUs aren't that bad, and most games don't need much to be fun.
The device is weird because it strikes me as the perfect HTPC, and yet it isn't really marketed as such.