Very same thing said when

TV was limited to 720p and some of us wanted it to go 1080p. Funny how before Apple embraces something it doesn't make much sense... but after they move, it makes great sense (go back and look at 1080p wish threads when 720p was Apple's max, or bigger screen phone threads, or NFC, or even front-facing "iSight" cameras when iPad 1 was launched, etc).
Why bother with a 5K iMac since we sit the same distance from the non-5K iMac screen? Why bother with retina-screens at all when we look at them from the same distance as non-retina screens?
4K is the next big thing in screens. If it can't make sense to us today, it shouldn't make sense when Apple embraces it either. BUT, like bigger screen phones or 1080p or 5K iMac or NFC or Retina screens on anything or FaceTime cameras on iPads, our collective sentiment will "evolve with the times" as soon as Apple decides to go there.
That said, I'm much encouraged by this rumor. The hardware must lead; it never makes sense for the software to come first. Personally, I don't really care if there is ever 4K content in the iTunes store; 4K playback means sharper pictures on 4K screens, our own 4K content shot on 4K camcorders will play back that much sharper, and so on. Eventually a Studio would be tempted to test 4K movie profitability; it they make a profit, they'll do more. And competition will want to compete.
There's no downside. The "1080p is good enough" (or the "no one will be able to see a difference") crowd could still enjoy their 1080p to the fullest, as better hardware can always player lighter software to it's MAX. Even the "720p is good enough" crowd could still enjoy their 720p video to it's fullest too... just like older software written for Macs several years ago will run just fine on brand new Mac hardware just made. My current

TV plays my choice of 1080p, 720p or even SD video. Should a 4K option come along, I'd expect it to simply be one more option (not forcing anyone to buy a 4K TV if they are happy with whatever TV they have now).