FWIW, upper level (XT/Ultegra and above)Shimano rear road and mtb hubs have used 3/16 in balls for some time. Not enough riders were wearing out hubs fast enough to support Shimano's program of planned obsolescence, so changes were in order. In the case of the XT FH-M770, the free hub body shatters prematurely before the bearings fail, so the longevity of the bearings is a moot issue.
Disc brakes put more stress on hubs than many people think.
Depending on your personal power output and the vertical component of your riding, hub shell failure and bent axles are far more likely than bearing failure.
Awaiting test reports-