Apple's Rip van Winkle slumbers in in the Mac Pro space were in part aided by AMD lack of viable alternatives for many years. There was measured, slow progress in the workstation CPU space. That is almost completely changed now. AMD and Intel are basically at 'war' now on the competitive dimension now. The add-in-card compute GPU space is heating up also.
the $3K > 1TB RAM capacity tax thing is completely detached from 2020 dynamics for a very sizable fraction of the overall workstation market ( which doesn't necessarily need > 1TB of RAM. ).
It probably doesn't mean a return to 11-14 month upgrade cycles but the 3 (or more ) year slumbers would probably basically kill of f the product's user base over time.
iMac Pro before WWDC is viable if Apple is just doing a straightforward iteration.
Xeon W 2200 CPU. already "released" by Intel. Should be in readily available volume by March-May.
Vega II GPU .... errr it is shipping in Mac Pro 2019 so volume ability constrained how? (***)
Thunderbolt 7500 ( Titan Ridge ) controller .. .again shipping in several Mac 2019 products now.
512 GB DRAM. ... already there in W 2200 series. Don't need a future Intel one to get there.
"better HDR support" ... if just added a LUT adjustment (and enable certified support with one or two colorimeters ) to the current display more than few folks would jump for joy. Don't need a fancier lighting system; just better adjustments of the one they got.
XDR chassis should be no where near as a priority as putting the RAM door on the iMac Pro. Drilling a hundred holes into the aluminum case and still not allowing RAM access would be hugely disconnected from the target dynamics in he market right now. (the XDR doesn't have any microphone , speaker(s) , or camera which pragmatically the iMac Pro is extremely likely to keep. ) . the XDR chassis also has a $999 stand that the iMac Pro needs like another "hole in the head". The XDR back is trying to mitigate a relatively small amount of heat and enable the use of two really small , low speed fans to cover a few double digit watt "hot" spots. the iMac Pro has order of magnitude different heat issues to deal with. Nor are the holes going to be primarily aligned with the dominate air flows needed to cool the system.
The larger and more complicated departure from the current iMac Pro chassis the longer and more protracted the trip through Apple Industrial design. That is just extremely likely going to be a greatly bloated time to market timeline. That is exactly not what the iMac Pro ( or Apple ) needs right now.
What Apple needs is an more affordable iMac Pro. Not extra flourishes to drive the cost substantially up. Apple could move the core count "down" the line up to inject more value take the new 10 core priced like the older 8 core part and start off with that and simply just shrink the core count line up. (i.e., 10 , 14 , 18 ). Prune the Vega II VRAM to 16GB and prune off the Infinity Fabric link. both of those should shave a ton of cost off the part. It would be a small delta over what have now, but it would also be shipping in reasonable time. ( Apple's primary fail over the last 10 years is far more failing to act than in what they shipped. )
If the iMac Pro slides to WWDC ( or later) then a shift to AMD would be more likely (although not guaranteed). If Apple 'bet the farm" on Intel W 2300 ( "Ice Lake" ) then it is probably in trouble for anything than a very late 2020 debut. ( and apple would be on a 3 year cycle which is more than problematical for them. Customer base bleed would grow. ). if Apple is going into a another 2 year delay cycle for the iMac Pro that might be worth it to take the short term reputation hit on doing sloth upgrades. Passing the two year mark on the iMac Pro puts them in the "dog ate my homework" status this Spring as to why they don't have anything. There are zero major component supplier to point to as to why they have nothing.
As for iMacs those too could/should have parts this Spring timeframe. No deep seated need for WWDC. The Comet Lake 10 core parts
seem to be in trouble , but the iMacs don't desperately need 10 core parts. And those won't possibly work anyway. If Intel releases the rest of the desktop line up and hold those 10 cores for "later" ( does a soft release for the hype and back fills later) then the iMac too should be "good to go". ( Apple needs a better $/GB storage solution to drop the HDDs completely there but the rest of the major components are would/should be available. AMD or Intel on the CPU path. )
(***) Apple could try to wait to sync up some late 2020 MPX GPU module updates to what would go into the iMac Pro an affordable more gamer focused "big Navi" , but that isn't likely to 'win' much for the length of the delay to get it.
Or Apple could technically walk the iMac Pro GPUs backwards and cover them with the 5700 and 5700XT ( although Apple might be able to tag them with something akin to W5700 and W5700X ) and just talk up the Display Stream Compression and pawn off the new XDR compatibility on those new GPUs.
( and the iMac gets stuck on 5600 level down clocked GPUs and maybe a VRAM relatively trimmed and down clocked 5700 )