Upon evaluating other alternatives, I opted for lunacy. I invested money in an engine refurbishment for my 210,000-mile F31 320D, including a new timing chain, oil pump service with sump removal, walnut blasting, cam cover replacement, water system overhaul (pump, thermostat, various hoses, tank, radiator), pulleys, DPF flex pipe and an additional ZF gearbox service.
Several discoveries:
A regimen of consistent and proactive oil changes has yielded benefits. The oil pump remains in excellent shape and was not replaced; the turbo is in wonderful condition, and the engine inside is exceptionally clean. The garage that has serviced it for me over the last years has evidently performed the task correctly.
Nonetheless, the maximum lifespan for the timing chain is 210,000 miles. The previous one was deteriorated, exhibiting greater wear laterally than longitudinally, which poses a greater risk of unexpected snagging and snapping; hence, it was unequivocally time for a replacement. The N47 has performed admirably.
The water system required replacement, however the radiator itself was not particularly problematic (it was replaced anyway for assurance).
An earlier EGR replacement 100,000 miles ago (to preempt the recall not being conducted on older vehicles), extensive long-distance travel, and the avoidance of low-quality fuel have led to negligible carbon accumulation over the past 100,000 miles (refer to the photographs below). The walnut blast was unnecessary, although I opted to have it performed while I was there.
The outcome: it is currently a 215,000-mile vehicle, operating with remarkable smoothness.