An affordable video card is totally capable of outputting 4k or even 8k video with no problem.
Encoding that or playing video games or using it for totally unrelated things is a different story though.
As you're posting as AC maybe you don't even WANT an answer. And now when you will likely get multiple will that help educate you and reconsider? Not likely. Because it's not a card FOR YOU and that's all that matter for you. That doesn't mean it's useless for everyone else.
Of course people will buy this and can afford it.
A friend just bought a GTX 1080 and a 34" 21:9 100 Hz G-sync screen (and the rest of the computer including the much more expensive Samsung Pro 950 drive and he will likely end up having the HTC Vive or another VR product too), he can afford this. Do he need this? NEED? Guess no. But of course not being able to pull off 4K gaming is an issue for him and as such the plan have seemed to included two GTX 1080 though I think it's better with one card which mean that he actually "need" something BETTER than this. Maybe this get close to 60 FPS gaming on 4K though.