The new Mac Pro is likely just a stopgap measure until they figure out a way to bring it up to the capabilities of the older Intel model, i.e. supporting more memory. They had the redesigned Mac Pro housing already, and they had the tech from the Studio, so why not make it available for users that prefer this form factor or require the PCIe slots?
Apple knows very well that copying another Mac's hardware with its restrictions and performance (and adding slots that are missing GPU support!) isn't going to make for an exciting product. But they surely had the plan for where the Mac Pro will be heading well before releasing it gimped like this.
If I were Apple, I'd be designing the next ASi iteration with an option for DDR5 memory slots in mind, and I'd offer an upgrade service where customers bring in their Mac Pro 2019/2023 in for a mainboard replacement and a yearly mainboard-replacement "upgrade" path is established.
I am convinced Apple won't ask us to replace the entire Mac Pro, and I am also convinced they'll extract as much money from their customers as possible, so offering that mainboard upgrade service makes perfect sense.
At that point the distinction between Studio and Pro will be clear: At the very least the Pro will support double the memory and more, and I assume there will be a chip beyond the Ultra that will be Pro exclusive. Since the naming scheme is already at a limit (what could be better than Ultra?) they'll call it something like P1 (performance) which allows for another Mac Pro exclusive series with varying performance from the P1 Pro/Max to the P1 Ultra.
And then instead of being forced to follow the yearly M release cycle -it would look silly if the Studio got the lastest M release and the Mac Pro didn't- they can establish a separate, for example 3 year cycle, so that they got a couple years in between Mac Pro releases.
Perhaps there won't be any user-upgradeable memory at all and the P1 will just double the max memory config from the Studio. I am hoping for more memory configs but 384GiB+ would at least be better than the measly 192GiB we get now.