From that video the cooling system is pretty much unchanged, Fusion Bay and connector gone, and primary SSD is soldered to board at least on the stock configurations.
There are reports that the 4TB and 8TB Custom Order options may have an additional expansion connector with a second SSD in area that the video outlines at 4:57.
There is
no second SSD. There is only one SSD in a T2 implementation. Apple's "SSD Modules" are more accurately labeled "NAND daughtercard". The SSD controller ( the 'brains') are in the the T2 chip. The cards are "dumb". It is just some NAND storage chips and a communication buffer (so that T2 can talk to the chips). Essentially what Apple did was chop what is usually one logic board in a conventional SSD into 2-3 pieces. Pragmatically the "SSD Module" is an internal component to the SSD.
The upside of chopping it into pieces is that if the NAND chips wear out or fail you can replace those chips. The key part of the SSD though ( the controller) is soldered to the board.
Due to T2 chip the second SSD in that connector is likely paired to the motherboard through encryption and there's most likely zero chance of using an m.2 adapter with another drive even if it is not soldered.
Yes that is not a m.2 header. But again it isn't a SSD that a user could connect if that header was present. Only Apple "SSD Modules" would fit.
A bigger problem though is that the size of the space provided for the header (and that there is only one header) suggests that to get to 4 and 8 TB Apple may be doing some hocus pocus and bonding both soldered NAND and daughter board NAND to get to those capacities. Which means if get a failure in the soldered NAND then the board is just as 'toast' as if the header wasn't there at all.
Gobs of space where the 3.5" HDD and they do absolutely nothing with it. Wow, a head shaker.
This is a "shuffle it out the door" system.
Not sure if you could take a genuine Apple SSD board and stick it in the extra expansion connector (on models where it is present), but that would be a pretty niche situation.
It isn't just any board. It would have to 'twin' pair to what was soldered on the logic board.
It is impressive that Apple manages to run all of these components using a 300W power supply unit. In addition to thermal constraints, the maximum wattage of the PSU is another factor that likely limits the allowable boost clock speeds of the GPU and the more powerful CPUs
Impressive is a stretch because the cooling system probably can't handle anything over 300W. AMD's spec list the TDP for the GPUs at 130W . The intel 10 core CPU probably can very easily burst into the 145W range . 300W is a bit weak for the top end BTO components. ( 10GbE will incrementally contribute too. Throw in TB providing power to a couple of external devices . )
Apple could have flipped the fan to the other side of the midline so it soaked up that cavernous, empt 3.5" HDD space. It would have been a bigger fan. ( cut some more inlets ) and gotten to a higher power curve. But no. They dogmatically clinged to the old case design down to the fan mount points.
