The concept "the editor of a category" has no correspondence with reality. It's like "how do you find the square root of asparagus?"
Reality is, there are always hundreds of editors who CAN edit in ANY category. Most of them will never have edited any particular category; however, most of them spend much of their time editing in categories where they have never edited before.
So, who will be the NEXT editor to edit a category? Editors choose for themselves where to edit; nobody attempts to track their choices; nobody CAN predict their choices.
Rather than micromanaging editors, our community leaders lead by example -- that is, edit. It's a far more efficient, and far more EFFECTIVE approach, and that's very important. But it is not at all PREDICTABLE -- and that's OK, any effort spent trying to predict it could better be spent doing something constructive.
And it is not at all CONTROLLABLE -- and THAT'S extremely important. a controllable process will be taken over by control freaks as soon as some value is seen in controlling it: and (rightly or wrongly) many spammers see a great value in controlling the ODP.