I don't like comparing with non-automotive applications.
Price point, sump size, temperature range, contaminants... are just not comparable.
Oil flow, oil pressure, oil temperature, and wear surface 'area' are what is being balanced to use those thin oils. Also pushing the change interval, base oil selection, and additive technology with these newer oil specifications.
Waiting on practical affordable turbine-powered cars/motorcycles, or magnetic vacuum wheel/cv/ujoint bearings.... feasible?
Various boutique oils have non-SAE grades(usually racing oils) that are thin. Non-SAE grades need to be defined by the manufacturer.
Too thin oil? parasitic drag from higher volume oil pump, or too cool oil temp from oil coolers, or too much bearing surface area, or overly large sump, or ....
At what point does it stop?
Should I plug in my ATF, oil, PSF, differential, and engine block/coolant heaters when it is 95°F outside, to increase efficiency, efficacy, and reduce cold-start pollution... all while consuming coal/oil/frackedgas/fukushima/chernobyl sourced electricty?