So, maybe I'll try to make my point once more. Let say A is interested to be mod in a science subforum. At first A should get 6 recommendation from existing mods and from admin. Certainly this will filter the quality of A. After 6 people (other moderators and admin) agree, A should get public support. If A doesn't get public support, A will have continuous problem with public. And so, for the sake of his quality, A could be an advisor (non-executive moderator / indirect moderator) to avoid clash with public.