Sorry, this isn't particular to the sensor. I hope Nikon/Toshiba is really able to control noise while upping the mexapixels.
I bought a D5100 in early 2012. I tried it at the camera store and liked what I felt there. It wasn't till I got it outside and went to use it "for real" that I noticed what would have been a deal-breaker: No Depth of Field Preview! I have used a bunch of Nilons over the yars -- they all had a DOF preview button to the right of the lens mount. A (D)SLR without a DOF preview? Why would Nikon leave off this most useful feature? They don't seem to have added it to the D5200.