This is huge, but subtle. For the first time, the SI units are no longer relying on unit prototypes that can only be copied. Given the new definition of the SI

This is huge, but subtle. For the first time, the SI units are no longer relying on unit prototypes that can only be copied. Given the new definition of the SI units, decent enough lab equipment and enough time, any lab can now theoretically manufacture its own references to arbitrary precision, no matter where they are in the known universe. There is no longer an insurmountable limited incurred by the precision of the local copies of these references.