Not really, remember on the nMP 6,1 Apple uses only video output from GPU1 to drive all 6 DP1.2 output on its TB2 ports, a TB3 nMP having 6 ports would require 12 DP 1.2 Signals to feed the 3 TB3 controllers (only acccept DP1.2 as older TB2 but twice signals), this case the existing 6 D.P. 1.2 paths on each GPU are enough using BOTH GPU Outputs.
So Apple actually only needs to redesign the Main Motherboard connector to input video from both GPUs, this also makes sense since allows Apple's HW R&D teams to test the nMP 7,1 on the older DX00 GPUs before arrive the the next Gen of AMD GPUs.
I am sorry, this is complete and utter gibberish.
The 6,1 GPUs were developed on cMP, we know that because 7970s got called "D700" until Apple changed subsystem vendor id to differentiate.
Apple isn't full of idiots. I guarantee that they have 6,1 and 7,1 mule systems that have PCIE slots. No way they could ask all GPU options to be created on their silly form factor for tests. Even asking that they be presented on MXM would be silly.
And nobody with any sense of how electronics works still believes that Apple, out of the kindness of their heart, is going to keep 7,1 GPUs backward compatible with 6,1.
Please, don't feed the delusions by trying to make it sound possible. It ain't gonna happen. New CPUs will have different pin outs, going to different PCIE lanes. New GPUs (hopefully) will have different spec DP and HDMI outputs. NVME vs. PCIE SSD routed through GPU circuits. TB2 vs TB3 ports different, different signals, different wiring. BIOS not on cards, in main boot efi, to make cards work in 6,1 would require new EEPROM setup on cards that works with older 6,1 BIOS/boot efi. Replacing cards in nMP requires ability to deal with delicate connectors and thermal paste. Dare I even mention the 2 different styles of Torx bits used to secure the GPUs?
The list is very long and still we have "well, just maybe, you never know" nonsense like this. Aside from all of the obvious reality that 3 more years of tech advances spell out, how about we just use good old common sense.
What direction has Apple taken with everything they build? (pick one)
1. Easier to open, readily available upgrade parts through 3rd party retailers, encouragement to keep older machines useful. OS drivers available to keep all brands & models working optimally.
2. Artificial obsoleteness through driver restrictions. Soldered down CPUs, GPUs, and RAM chips. Glued, taped, and riveted housings to keep the "mucker abouts" out. Reintroduction of 5,400 rpm spinners that risk breaking things to get back out. Lack of available parts through anywhere but official repair channels at absurd prices that makes scrapping a 3 year old machine cheaper than fixing it.
Everyone put on your thinking caps.
Because the cMP has such a great TB upgrade path...
I'm putting a GTX1080 in my cMP today. 6,1 is still mired in 2011 tech due to silly design choices. Do you really want to compare upgrade paths?