... or those proprietary Guildline-relays: latching relays which press a goldplated copperfoil on gold plated copper traces on the PCB, which results in <50nV emf error ...
This sounds a lot like the way Tek made switches in their old gear. It was used extensively in their plugins, both on scopes (like the 7000 series) and general purpose T&M gear (TM 500 series).
Basically, they had these little metal leaf springs they would rivet into the PCB. Connected to the other end of the leaf (by a piece of insulating Teflon) was a gold plated copper "fork" contact. It was U-shaped, so when the leaf spring was pressed down, the U would bridge two adjacent pads on the PCB, completing the circuit.
So they would have as many of these contacts as needed, side by side in an array. Over top of this array they affixed a plastic cylinder that had ridges placed wherever a particular contact was supposed to be closed in a particular position. (The ridges would press down on the leaf spring.) So, as the cylinder rotated, the entire array of contacts would open or close as needed for that particular switch position; essentially, it worked just like a music box!
The U contact kept firm pressure with the PCB, so it was very low resistance. It was also small, so it had very low capacitance and inductance (hence they could run high frequency signal over them as well).
I know in several instances it was used for selecting divider taps in some of their calibrators. They eventually developed an electronically controlled version of the technology (they used some sort of micro miniature solenoid) for their GPIB controlled TM 5000 "all in one" scope calibration plugin.
Here's a view of a board with the cylinders in place:
Here's another board showing the contacts: