Haha that's hilarious. I had a guy at best buy try and sell me a 4K tv, but I asked him if he thought content providers will ever have the bandwidth to be able to broadcast 4k, and he said quietly "no, but that's not really a selling point" It's really cool if you have a 4k camcorder though. I'm sure it's putting a HTPC through the wringer though.
I heard that the Galaxy Note 3 is capable of recording 4K video (but I don't think it's capable of playing it). So far, that's the only thing I know that could record 4K video. But in my case, playing 4K video on the HTPC wouldn't put it "through the ringer," considering it's got some pretty nasty specs (which I cannot disclose at the moment). Since I use it for gaming (as well as playing movies on 1080p Bluray), I guess I would call it an HGTPC, if you catch my drift.