SAMSUNG LTN156FL02-L01
http://www.panelook.com/LTN156FL02-L01_SAMSUNG_15.6_LCM_overview_23360.html
http://www.ebay.com/itm/4K-LED-LCD-Screen-Fit-15-6-LTN156FL02-L01-eDP-slim-3840x2160-UHD-Lenovo-Y50-70-/271692456983
The high DPI is nice, but the ration is 16:9. I was looking for a 3840x2400 16:10 (WQUXGA) display for a laptop but I came up empty. IBM did make a 22" version of the 3840x2400 but that has been the only panel in that resolution that I have found so far. A disadvantage of the IBM display is it's slow refresh time of 41/48Hz.