Might lean toward postproduction studios' use cases?

No GPU support, but the slide during the presentation showed extended storage (4-8xNVME to PCIe adapters are fairly inexpensive I think), SDI video ingestion, ProTools HDX cards (music I/O and DSP), 25GbE card, and I think a fiber channel one. Since then a third-party company announced a networked audio card.

Possibly some special-purpose accelerator cards; IIRC the first-party Afterburner cards on the last mac pro were FPGA-based; video acceleration is now built into the M2 chips.

I think most of the extra ports that differentiate a Mac Pro 2023 from a Mac Studio Ultra on the spec sheet are on a small PCIe card included with the machine that stays in the top slot.