FEP-baf5: Administrator Collection
The reason why attributedTo was chosen is because there is prior art to using that property to represent a collection of moderators. You could make the same argument against 1b12 (that moderators should be the key instead of attributedTo), too.
The argument as to whether a custom property fits better is certainly valid, and worth debating. However, I would want to point out that keeping with prior art has the benefit of making this FEP much easier to adopt by threadiverse implementors.
