"Everyone would want a 4K display"
First of all you should never use words like that, speaking for everyone is not wise. Lets take an iMac owner, my fiancé, she has a 2010 27" iMac, are you saying that she will want a 4K monitor when/if Apple releases it. She doesnt even know what 4K is nor would she care less about it. Who do you mean when you say "everyone"? do you mean all the people on this forum, or this thread or the State of California? I would bet the majority of people in the USA dont know what 4K is, and the I can only speak for the people I know, most dont care. You are projecting your wants on others, and not just a small amount of others. You are projecting your wants on "everyone".
I love the idea of high resolution screens, and when you look how far we have come in the last 10 years, its interesting thinking where we would be 10 years from now. I think Apple may not follow the 4K bandwagon and do what they do best, Lead. They may use a higher resolution, like the Mavericks Wallpaper download, I believe that is 5K.