My theory is that they're going to release a new Mac Pro that's about half the size of the current one. Enough space for some PCIe slots, but otherwise smaller given the enormous amount of wasted space in that thing since moving from Intel to Apple Silicon. Guessing the rack-mount model, should they continue selling it, will be 3 or 4u instead of 5u.
I know everyone thinks they're going to just kill it, but I don't see it. Apple's move under Tim Cook has been to exhaust supplies (see: filling the Intel Mac Pro chassis with air and not updating the CPU), letting people predict its death (see: 2013 -> 2019 Mac Pro silence), and then redesigning it into something people want while utilizing it as an opportunity to segment specs across their SKUs.
The Studio will remain the high-powered creator machine, whereas the Mac Pro will be retooled into an AI beast.
Why people buy the Studio with the high ram config is actually the unified memory. This is unique to Apple. I'm not sure what Mac Pro would do with PCIe cards . It would be useless for AI because what you want is unified memory that can be used by the GPU/AI not just ram.
It is already a walking zombie, Apple clearly no longer cares about the workstation market, regardless of how many "I still believe" t-shirts get sold to wear at WWDC.