https://videocardz.com/newz/geforce-gtx-1060-with-gddr5x-memory-confirmed-to-use-gp104-gpu
 
Instead of reworking a purpose-built memory controller solution compatible with the GP106 GPU, the company has gone and carved the SKU from its existing GP104 silicon - which already supports the GDDR5X memory subsystem due to its implementation on the GTX 1080 (GP104) and 1080 Ti (GP102) graphics cards. 
 
The discovery came courtesy of a teardown on iGame's GTX 1060 U-TOP V2, which features a triple-fan cooling solution, 2x 8-pin power connectors, and an 8+2 phase power delivery design, via Taobao. Apparently, even the SLI fingers remain on the card, which if you'll remember, never where supported on NVIDIA's GTX 1060 - a result of iGame's decision to simply reuse their PCB design for the usually much more powerful, GP104-based GTX 1080. 
 
So NVIDIA has come up with a method to make a new card and get rid of surplus inventory.