I think the rule of thumb is to replace the fluid at 5K, after most of the break-in has occurred.
The thought of running the fluid further with all those contaminants is nasty. I've seen what lubricant contaminated with break-in debris does to bearings, and it's not good. I tried to talk to manufacturers, for them to go away from the "filled for life" trend that is pervasive in the automobile industry, and that a fluid change to get rid of break-in debris would go a long way with reliability of their product. Unfortunately, their customers are enamored with the "filled for life" feature presented to them. And the manufacturers chiefly worry about the warranty period.