Yes, dynamic range will increase but don't get too excited, since the increase is minimal.

According to

http://www.dxomark.com/Reviews/Detailed-computation-of-DxOMark-Sensor-normalization, the formula that relates DR and pixel count is:

DR(new) = DR + Log2 (Square root(N / N (new)))

Where

DR: Original DR

N: Original Megapixel count

DR(new): resulting DR

N (new): Downsampled Megapixel count.

Lets compare the values from the Nikon D810 to those of the Canon 7D MkII using the values from DXO Mark. (The value for DR to be used is the "screen" value, which correspond to the pixel values).

D810

DR (screen)=13.67

7D MKII

DR (screen)=11.11

Let's suppose that Canon produces a FF 50 Mpixel camera with the same quality as the 7D MK II, The DR (screen) will then be = 11.11

Now we apply the formula to downsample those 50 Mpixel camera to the D810

DR (new) = 11.11 + Log2 (Sqrt(50/36))

DR (new) = 11.11 + 0.237

DR (new) = 11.34

Results:

D810= DR 13.67 Stops

Rumored 50 Mpx camera downsampled to 36 Mpx = DR 11.34 stops

So, even with the increased DR due to the larger pixel count, the D810 will still have more than 2 stops of additional DR.