It is remarkable if Nikon just manages to achieve the D7000 ISO performance at 24 MPs. Personally I think the well is likely tapped for ISO performance on DX by and large. The reality is that the sensor size is likely at the point of bottlenecking substantial upgrades.
I would note some caution in using DXOmark's measures respecting ISO performance. DXO bases their score on "the highest ISO setting for a camera that allows it to achieve an SNR of 30dB while keeping a good dynamic range of 9 EVs and a color depth of 18bits".
Some have suggested this methodology is flawed as the numbers are fairly arbitrary. Note what is does not take into account, how higher ISO photos look. What happens when you try and recover detail from the shadows, etc.
I personally don't find that either the D3200 or D5200 have in actual fact, better ISO performance than the D7000.
That being said they did manage to squeeze around 2/3rds of a stop between the d90/300s and the d7000 so we'll see.