That the domain of desktops that you can swap out the video card and other parts.

To play 4K content is going to be rough as the GPU power can be very high. To be sure it will work, look at Nvidia 1070 and higher equipped laptops.

For me I'm going to stick to 1080p streams and let the TV upscale for now.
And yes I own the Amazon 4K Fire TV box. Quite a bargain at about 99 bucks. It has Netflix and more.