I bet by 60k, oil analysis would indicate all lubricating additives would be spent. By 100k if not changed....the metal shavings themselves would be the lubricating agents.
I just do drain and fills because I may want to keep the car through 150k miles in severe (desert heat) conditions AND be able to give or sell car to friends/family with added peace of mind.
Ill take that bet, but it wont be with my fluid, because Im not changing it. Theres no use to at 60k, or even 100k, and its not because Mazda told me so.
Metal shavings as the lubricant at 100k, ha, I needed that laugh this morning.