Also there is a lot in 1 given power supply module that can be mostly reused for other purposes. Even for my SMU thoughts, most of it will be just giving it a bidirectional output stage and current shunt. apart from the level of ideal output stability its just set current with voltage compliance limit or set voltage with current source limit. the smarts come from how you use that, the feedback chain is still analog, the sampling is technically independent,
As such I'm beginning by trying to make a more flexible ADC, then once that is covered, figure out how the output stage could get away with the current tracking approach to keep the output stage regulating with very low dissipation.
The keysight level SMU's seem to have a step response bandwidth close to 50KHz, so nothing too extreme,
Technically with a multi-slope ADC like I'm trying to help work out, you could have as many analog inputs as you can mux in, so having say 6 external ADC inputs would not be expensive to add to things, just slow down how many data points you can pull off a second for a given resolution.