With the iMac Pro already on T2 how much effort is required here? Apple also already has "in the bag completed" Mac Mini T2 , and Mac Pro T2. The rest of the entire desktop line up was already on T2. Where is the "Moonshot, rocket science, Buck Rogers" project here ? ( the Pro 5300 , 5500 , 5700 have been used in other Macs at different clocks to so no "bleeding edge" GPU driver work here either. ) Yes, there is some work to do here (different socket , different PCH, hodge-podge T2 NAND layout ). However, it really shouldn't be that complicated though that they hadn't done previously on other systems. .
The board layout is a bit different. There are fewer TB controllers to deal with. They can pilfer the 1 vs 10 Gb/E solution from the Mac Mini. The camera is off the iMac Pro; a camera from practically the same case. The updated SD Card reader was going to be show stopper problem?
This design should have be almost done last June-July ( in 2019 ). Pretty good chance Apple has just sat on it for more than several months. Even more so if they know they won't have a large scale iMac class Apple Silicon SoC to go to in most of 2021. (i.e,, the 21-24" iMac will use a different SoC than the 27" ). In that context, they would have even bigger motivation to 'slow roll' this as they have to fill in a gap.
If Intel and/or AMD delivered the binned parts a bit later and there were hiccups due to the pandemic ... the slide to this point isn't very surprising at all.
I liked the insight of this post. Brutal though it was. *dusts himself down.*
Azrael.