I really appreciate all of this. Ford Motorcraft Yellow is a Phosphate Organic Acid Type. This guy has a decent rundown of it all:
My unfounded assumption is that much of the complexity has arisen from two sources: 1) environmental concerns and 2) "extended service intervals". In an application where folks properly dispose of used coolant, flush old coolant before mixing new stuff in and change coolant at regular intervals, it seems like virtually anything better than tap water should work well.
I'll tell a story to illustrate the creep of needlessly complex and failure prone "features" into modern cars. I have been fighting a 3 year battle on my F150 hybrid vs the exhaust heat exchanger. Ford engineered a stainless heat exchanger with a plastic controller valve on top which, under the influence of a 12V control signal, directs exhaust through a separate flow path which HEATS the primary coolant loop. As you can imagine, bolting plastic electronic components to the exhaust pipe can fail in several fun ways: the valve can fail open, continuously heating the coolant and overheating the truck, the plastic proprietary "quick release" connectors can fail, quickly or slowly emptying the vehicle's coolant onto the road behind the truck. Notably, neither of these fail deadly conditions triggers a warning message to the driver until the engine overheats, BUT Ford helpfully installed two temperature sensors on the in/out coolant lines to detect the expected temperature increase when the valve is commanded open. This makes it impossible to remove the heat exchanger without some variety of code.
For over a year, the F150 community assumed that this loop heated the low temperature coolant loop so that the battery would work in low temperatures. However, we came to find out that in fact this heat exchanger heats the standard coolant loop for the express purpose of causing the heater to work slightly faster in very cold conditions (in a truck equipped with heated seats and a heated steering wheel, no less).
What's the point of that story? Do NOT assume that the cost in terms of complexity, particularly in the automotive world, has ANY relationship to the potential benefit.