With that absolutely GLORIOUS SOC breakdown from ReddDreadtheLead, I think I'm fully convinced of its capabilities. Now I just want to actually SEE it!
My speculation, per some of the earlier posts in this thread, would be something like this:
Black Joy-Con. (No other changes, not even to the sticks.)
Black Nintendo Switch Dock with LAN Port (Same as the Neon Red and Blue OLED Model), if this is part of the same family and the family already has a 4K dock, doesn't make sense not to use it.
A wraparound kickstand like the HP Spectre, same hinges as the OLED Model, moved to give the motherboard more room.
Possibly the same fan assembly as the OLED Model, but I think the old assembly from the V1 could do the trick with redesigned ventilation, so a larger exhaust at the top, and a combination of slim, OLED Model intakes at the bottom and ovular, Lite-esque intakes above the kickstand (this layout happens to line up with the existing intakes of the Dock With LAN Port.)
Very similar shell to the OLED Model, only possibly metal.
The same screen as the OLED Model, but maybe HDR capable?
While tempting to say this device should use all-new parts for everything, as I understand it this is still a device in the Nintendo Switch family of systems. It might not even have a different logo on the back.
I also think price optimisation would be paramout to its design, reuse as many components as possible without sacrificing graphical grunt, optimise supply lines, exploit economies of scale, because a LOT of the price of this device is going to be in the silicon, and that's pretty inelastic, so where they CAN save money to keep this beast under $500/500€, I think they will.
As for confusion in advertising, the OLED Model is always shown with its default White dock, I imagine the new model would simply always be shown with its dock being black. I also suspect the V2 could be discontinued so they can stop making its weirder, older dock, fan assembly, can focus everything on OLED screen orders to share between the TV capable Nintendo Switches on shelves. Or they could do a quiet redesign of the V2 with the OLED Model motherboard, fan assembly and dock and minimise external changes.
Either way, I WANNA SEE HOW THIS THING LOOKS BEFORE I DIE!
Edit: in case Raccoon sees this and starts to worry, I don't think it'll be any bigger than the OLED Model, and if it is, only by a mm from Joy-Con to Joy-Con, negligible.