As the 7900XTX only has cache dice and the compute die, it's not necessarily the case that you'd need an interconnect that isn't there to connect another compute die. We don't know enough to say the cache die interconnects could only be used for cache dice, or how much communication between dice was actually necessary - if the driver's in charge of distributing work, and atomic operations are rarely used, you might not need that much bandwidth. It's also not necessarily true that the final die was the one they were expecting to make - if it's decided fairly late in the design process that you don't need a massive interconnect, you can just leave it off to save some die area, and it shouldn't need everything else to need majorly rearranging as it would be at the edge anyway.
As for the reticule limit thing, being at 75% of the hard limit does indeed mean you're unable to respond to your competitor doubling their number of compute units - you've only got a third of the space you're already using to grow into, and more than a third of the 4090 is compute units, so you can't respond by doubling yours.
My source tends to be right about things when it comes to leaks, and usually quite a while before other people are, so I'm inclined to trust that they don't repeat things until they've been leaked the same information from several reliable people.
As for the reticule limit thing, being at 75% of the hard limit does indeed mean you're unable to respond to your competitor doubling their number of compute units - you've only got a third of the space you're already using to grow into, and more than a third of the 4090 is compute units, so you can't respond by doubling yours.
My source tends to be right about things when it comes to leaks, and usually quite a while before other people are, so I'm inclined to trust that they don't repeat things until they've been leaked the same information from several reliable people.
OS: Windows 10 64 bit Professional
CPU: AMD Ryzen 5900X
RAM: 48GB
GPU: Radeon 7800 XT
CPU: AMD Ryzen 5900X
RAM: 48GB
GPU: Radeon 7800 XT