Ive been following the topic on the Etracer, it looks like a well thought out unit, however beyond the price point of many.
This unit, well ive decided on the DIN form factor because my major pain point with the Roetest was that Large backpanel PCB (Expensive and non customizable). this current setup can be expanded to Seven metered supplies( Assuming heating is DC and one leg is grounded ) for example the G1 regulator card will feature an internal oscillator that can be disabled if required. the Rout of the unit will be 10Kohm, so nothing is stopping anyone from using that card for say DC offset control and superimposing their own AC on that. each bus will have the outputs and rails paralleled between multiple connectors, however all the differential signals are connector specific. and will be connected to a header. or routed to one metering card specific Din socket.
Another card in the making is a simple noninverting amplifier card, featuring +-100V 50mA and a output swing and a BW in excess of 10Khz. with again differential sensing for the current. This one could be used to supply low voltage for supressor grids, or even fast positive pulses for pulse testing tubes.
The supplies HV and high current will get their own back panel with H15 connectors. i went for these because they have the voltage rating to go over 350VDC. the Din 41617 connectors where my choice because i got a bounch surplus for the price of Fish and chips.
plus they are more robust in my experience. Din 41612 Connectors tend to have pieces of plastic break off and bend pins, if mishandled. DIN41617 conectors you can just bend them back into shape.