The Mac Pro (and the high-end Powermacs that preceded it) were always available in a dual socket incarnation, right up to the trashcan Mac.
The trashcan Mac Pro was announced almost 9 years ago. Apple today is a very different company. They've moved onto chiplet designed SoC's with little to no care about upgradability.
They have done this previously for dual socket Xeons. Historical precedence doesn’t necessarily hold here, but in fact, it’s been done on the “cheese graters” previously
They also water-cooled them but I’d bet a lot of money we never see that again either.
They've moved on to chiplet design. Don't disregard their clear direction to SoC's with non-upgradeable RAM, GPU, CPU.