Earlier quoted context omitted.
That's missing the point. If a human can manage to keep it within 100 feet of a desired altitude, an autopilot most certainly can; it didn't require new technology in the 2000s. Autopilots in the 1960s/1970s weren't seesawing all over the skies.
RVSM is overwhelmingly about instrumentation accuracy and precision, not pilot capability. [0] The pressure difference between 5K MSL and 10K MSL at standard conditions is 14.6 kPa. The pressure difference between 30K MSL and 35K MSL at ISA is 6.3 kPa. For a given amount of aircraft-to-aircraft variability in their precision altitude sensing equipment, the resulting difference in actual altitude is more than double i…
You’re talking about getting different aircraft to agree between each other.
The post upthread expressed surprise at an aircraft maintaining a steady altitude to within tens of feet. That’s been a thing for many decades.