I still fail to see why it wouldn't work. The only failure mode I can
think of is the case in which the emitter resistors are too small to
divide the load properly at low currents / high voltages.
Not saying it cannot work, but you'd need big expensive transistors
to make an active load for 200V at hundreds of watts.
I'm working on a power DAC at the moment, only going up to about 30V
and 30A, non-trivial when you want the same circuit to hold to the
output to nearest mV or mA
First version with transistors leaked and drifted too much, current
version being designed & built with MOSFET switched resistor banks
and analog power amp to make up the small stuff seems far more viable.
But here I'm drifting OT as I'm making a precision load, not a simple
test load, but that explains why my focus is more on the reliability
of an active load.
Recently I built a 1A current sink, while it didn't fail, it was
cooking a power MOSFET on large heatsink, but without fan, at
only 30W. So I pulled the plug at 20 hours operation. Then
realised I could use a bridge circuit instead of accurate current
sink. Side stepped a problem, finding a better solution
ordered $5 worth of precision resistors 10:1 ratio.