Two words: selfless dedication.
Sounds kinda grand but that's really what it boils down to. You want to see the directory grow and improve and are dedicated to making it happen. Throw in some good people skills, the ability to help others without ticking them off, and being good at finding and reporting abuse.
Of course knowledge of the directory, the larger picture, ontology, and great editing are all factors too, but that's the editall stage more than the meta. No one jumps right from category editor to meta, there are steps between, 2 to 3 depending on the person. Personally I became an editall/catmv after 1.5 years, then a meta 3 or 4 months later.