If you really wanted to not run the coolant pump until you'd got the engine a little warmer I would have thought a magnetic clutch like an aircon compressor would have been better. Although these days, maybe even an electric pump could be more efficient.
I’m not familiar with the impeller shroud you mentioned, but I looked it up and the description seems to agree: “This pump includes the shroud and control valve to restrict flow while the engine heats up.”
Whether or not it affects the time required for the heater core to be operational would depend on how they decided to route it, and if the solenoid offers variable positioning. I imagine it is variable, otherwise they’d create thermal shock every time the engine heated up and the pump suddenly started flowing colder coolant through the block, so technically it should be possible to fully replicate the general functioning of the thermostat and heater core. Now that I think about it, it’s most certainly variable and it’s why they didn’t go with a clutch system.
I hadn't thought about the thermal shock thing but I did wonder how it could possibly help the coolant warm up if it's not circulating at least through the block. The engine doesn't warm up evenly.
My only other guess is that it’s not 100% on/off, like maybe a bit is still allowed to flow when “off”, but then it would still need to bring the entire coolant mass up to temperature so I’m not sure how that would be a benefit for faster warmup. Either there’s some clever engineering I’m not seeing, or you’re buying a few points of regulatory compliance for them by needing to replace head bolts and gaskets sooner.