The majority of the buying public can barely notice the difference in quality between 720p and 1080p on their TV screens. I doubt 2160p will succeed beyond the AV enthusiast base.
Beyond 1920x1080, there is no economic advantage to sell monitors at 16:9 ratio because they will not share the same panels as TVs, which is the ONLY reason 1080 monitors are so cheap. At 2560x1440, the massive cost benefit disappears in comparison to 2560x1600 and that is why we are seeing relatively more 16:10 computer monitors at 30" and above. At these sizes, there is a stronger demand for 16:10 panels because the professsional market prefers this aspect ratio for work. Since there is no TV market, it makes more sense for manufacturers to sell the same 16:10 panel to consumers.
In summary? Long live 2560x1600!