I think @Roman is the best person to weigh in on core extensibility here.
There is a general concept though that kind of makes sense to add @eviltrout / @codinghorror . I think moderators should be allowed to add quick notes on any flag at any state.
That way they could have a clean “lightweight” way of handling edge cases.
Eg:
(Sam) I think this flag is valid but I am not sure
Then when Jane sees the flag she can act in confidence knowing Sam was on the fence anyway.
Requiring 2 moderators may not be what you want @mint_saxon, this may be simply the case where you want your moderators to have some extra metadata. Having mods need to reach consensus on obvious spam and abuse seems way too heavy.