Wrong again. I have no idea what you find so complicated and confusing about this.
Currently, the top 15" rMBP uses the $623 part I listed. This is the
I7-4980HQ. It's the 4th gen i7, released in 2014.
In 2015, Intel released an upgraded part, the 5th gen, for the same money. This is the
i7-5950HQ. Iris Pro and everything. In 2016, Intel released again an upgraded part, the 6th gen, for the same $623. This is the
i7-6970HQ. Again, all of them cost $623. This is the top option.
If you look on everymac.com, you see the full list:
MacBook Pro "Core i7" 2.2 15" Mid-2015 (IG)2.2 GHz Core i7 (I7-4770HQ)
MacBook Pro "Core i7" 2.5 15" Mid-2015 (IG)2.5 GHz Core i7 (I7-4870HQ)
MacBook Pro "Core i7" 2.8 15" Mid-2015 (IG)2.8 GHz Core i7 (I7-4980HQ)
MacBook Pro "Core i7" 2.5 15" Mid-2015 (DG)2.5 GHz Core i7 (I7-4870HQ)
MacBook Pro "Core i7" 2.8 15" Mid-2015 (DG)2.8 GHz Core i7 (I7-4980HQ)
See the 4980HQ last? That's the best option. Intel produced an upgrade in both 2015 and 2016, for the same price.
But if you take the current entry level, the 4770HQ, sold for $434, you'll see that Intel had upgrades for that too. It's the
i7-5750HQ, 5th gen CPU, released in 2015, has Iris Pro, same $434 price. Followed by the
i7-6770HQ, same price, launched in Q1'2016.
Clearly, Intel did provide the chips. In particular, they provided what seems to be a full complement of 5th gen CPUs suitable for the 15" rMBP, in 2015. Then all the Skylake CPUs are listed as released in Q1'2016, not "just released".
This story that Apple didn't update the 15" rMBP because they had no CPUs from Intel seems a complete fabrication.