Congratulations, you can quote completely out of context by stripping of extremely relevant adjectives. Playstation (PS) Navi is coming in 2020... Sony said so. Sony's and Microsofts Navi has a pretty good chance of being substantively different.
Playstation Navi is a custom package for Sony, not a consumer PCIe GPU... The E3 presentation is for Navi-based consumer PCIe GPUs...
I know Steve Jobs is not with us anymore, but I do remember what happened last time someone tried to announce a GPU AND talk about it being in the new Mac... I believe it was ATi & Apple just stopped using their GPUs for a good number of years after that...?
AMD might not want to take a chance on repeating that...
(...especially if they are hoping to land Intels spot in supplying CPUs to Apple...)
As for AMD's Q3 Navi aimed at PC's ... it is only that 'some' aspect of Navi was shipping in Q3. Not a complete 'top to bottom' line up. AMD is going to some updates to the bottom end of line up.
https://www.tomshardware.com/news/amd-radeon-rx-640-radeon-630-graphics-card,39325.html
and that probably means Navi won't cover those. AMD itself has basically said that Vega VII isn't going to disappear any time soon. (Navi in 2019 doesn't cover that) So it is highly likely going to be a relatively narrow subset of Polaris that Navi will cover in Q3. More likely that is closer to the entry card for a new Mac Pro than some "whole line up" show stopper. Mac Pro would perhaps get a better entry and mid range card with Navi, but if Apple goes with Polaris+Vega ( stuff they already have ) it would not be surprising if they ship in Q3. If the rest of the system was sliding deep into Q4 than Navi makes some sense. However, Apple "holding up" Mac Pro primary on Navi really doesn't.
Never said the whole Navi line-up was fo Q3 2019; I would expect some of the line to be available on release, and some more down the road, especially Navi 20... Nvidea doesn't release all of a line-up at once, AMD does not need to either...
If they were doing the next Mac Pro "right" that would be increment update later they could do several months after release.
If you look at the posts I have done with potential specs for the forthcoming modular Mac Pro, you will see when I reference Navi, I note that Navi 20 ('Big Navi' that will also be the basis for the next gen of Instinct GPGPUs) would probably arriving sometime in Q2 of 2020...
The GPUs I expect to be available when the modular Mac Pro ships...
- AMD Radeon VII, 7nm Vega 20, 60CU, 16GB HBM2
- AMD Radeon RX 3090X, 7nm Navi 20, 64CU, 16GB GDDR6 (available Q2 2020)
- AMD Radeon RX 3080X, 7nm Navi 10, 56CU, 8GB GDDR6
- AMD Radeon RX 3070X, 7nm Navi 10, 48CU, 8GB GDDR6
There are a few Navi 12 GPUs (less CUs than above, 4GB RAM) rumored as well, but I wouldn't think Apple would carry a large number of SKUs for BTO GPUs, especially lower end models...?
The iMac pro got an update in March-April . The Mac Pro did not; not even a peep.
It is highly likely that Apple has a very significant difference in priority orderings. And their order probably counts more toward wither the product is canceled or not. If the iMac Pro got terminated that likely wouldn't bring the next Mac Pro any faster. In fact, it would probably indicate that the Mac Pro is in even deeper peril.
I just feel that if Apple can manage a proper modern Mac Pro personal desktop workstation (with matching 'Pro' display), there is no real need for the iMac Pro... I think Apple wanted Mac Pro users to shift over to the iMac Pro & it did not take off as well as they wished so now they are back to making us a new Mac Pro... My personal opinion...