Apple is super fucking rich, I wouldn't be surprised if they are ready to pay TSMC enormous money to make monster monolithic dies, and Mac Pro could be single-socket only, packing >128 cores into one socket.
You need lots of memory too. Maybe not an issue for the desktop. If they doubled the SOC for 16 cores (8 hot/8 cool) and 32GB of RAM that would be a decent Mac Pro.
But plenty of people want >32GB of memory, I routinely use machines with 256GB. No way you can get enough RAM into the SOC. Large core counts are even harder, because speed of light means you need a new on socket switched architecture, memory on the other side is slow to access etc. TANSTAAFL.
They probably won't use DDR-on-package for Mac Pro tier chips, so RAM could be whatever they want, they could put an 8-channel DDR4 controller onto the SoC, or even DDR5 if they don't rush it to market ASAP.
But it would be cool if someone did a tiered HBM+DDR system already.. (AFAIK Fujitsu A64FX is HBM-only) maybe the Mac Pro could be that. I kinda wish AMD did that though.
