By the end of 2022, AMD will have RX7900XT with >15,000 cores. AMD has already demonstrated how it'll be done in AMD Instinct MI250 today.
the MI250 presents as
two GPUs to the software/OS. I'm skeptical that if the rotate down a tweaked version of CDNA down to the mainstream space that you'll end up with the same naming sequence for those cards. The dual die cards will more likely be skewed more to "compute" ( whether crypto, AI/ML, non-interactive render) rather than interactive 3D real time interactive rate.
Presenting as two GPUs with a single package is more so just better "Packaging" than Apple's W6800X Duo. Better thermal envelope and more efficient board area usage.
However, for games, 3D interactive , etc app that have little infrastructure to put two GPUs to work on a single problem with no visual/app glitches there won't be as much impact. ( stuff like SLI / Crossfire have always been a bit glitching at 60Hz targeted normal refresh synchronization rates. Crank that even higher and it is likely more glitchy ).
The latest rumor that Apple "officially" leaked through Information no longer mentioned 4x M1 Max dies. It still mentioned 2x M1 Max dies but 4x dies will be based on the successor of M1 Max.
It can't literally be two M1 Max dies as there is no interdie connect infrastructure on the dies. It would be a different die. Since it is a different die there is some chance that it would just be just one die. Especially, if they abandoned getting to 4 die 'worth' of core count in the M1 era.
One option would be to just scale up like they did with the M1 Pro -> M1 Max. Just add more GPU and CPU cores. Drop one of the NPU+Video decode clusters ( the one at the 'bottom' between the extended GPU core stack and the die edge and just start from there (somewhat in a mirror image GPU+Memory controller + CPU core + subset of I/O (no need for extra secure processor , SSD controller , swap some Thunderbolt complexes for simpler generic PCI-e v4 , etc . ) . Apple probably would be up near the reticle limit ( > 700mm2 range ), but they'd be avoiding packaging overhead costs and would get a higher Perf/Watt. End user costs would probably go up ( paying for defective dies can't use) , but is Apple really pressed about how much they are charging for upper end M1-series SoCs ; not much.
In short, build an even bigger GPU complex ( this time 64 cores) as the nucleus and wrap the CPU cores and I/O around that.
Second option would be to again 'nuke' (actually more so 'repurpose' ) the second M1 Max NPU+Video decode into Interdie connect infrastructure . But those wouldn't be M1 Max dies anymore. The combo of the two dies would still have dual NPU+Video decode , but would have pushed the collective CPU and GPU core count higher. If packaging costs are offset by higher yield rates then might save the end users a bit of money get to more bang for buck out of the wafer starts they have access to.
In the first case, the "inter CPU/GPU complex " networking is all on the die. They might still segmented it into two "zone" so could turn a major part of the network and components off when not needed. In the second case, it is a "walk before run" approach to evolving a interdie networking solution. If capped at just two dies it is easier to solve than a "fully connected" ( three links to three partners) solution. Taming the NUMA issues of just two is easier than four (or more).
If just "exactly clone" two M1 Max'es together then will not have much of flexible , very high bandwidth I/O left in the combo. ( a couple of x1 PCi-e v4 lanes isn't much and Thunderbolt 4 is limited. Nothing like x16 PCi-e v4 (or better) ). To get to substantively better I/O then they will need something substantively different than a M1 Max die. Period.
There were four "Jade family" code names. Jade (M1 Max) , Jade-chopped ( M1 Pro) , Jade2c , and Jade4c . There were likely
four different dies. Saying they would take four Jade dies to make a "Quad" product would beg the question as to why would need implement a jade4C solution ? Maybe it was "muddled" code words before but the Jade and Jade-chopped are obviously different dies. Super high degree in overlap in basic design, but
two separate die masks being used. Therefore, highly likely that Jade2C and Jade4C are also two separate die masks.