Im curious as to the chances that Cersei or Margaery could demand a Trial of Seven, as used in the Hedge Knight novella, especially cause theyre being held captive by the Faith and a Trial of Seven is a religiously inspired trial by combat.
Its not abundantly clear as to who can and cannot demand such a trial and it could be in Margaery's interests to so in order to possibly level the playing field if a Super Mutant Gregor Clegane does enter the picture as hes like to do. Though at the same time this is an extremely rare and widely unknown rite so they may not even know of its existence, its only known use was almost 100 years prior.
Regardless though, I would love to see it be used. It would simply just be an awesome fight, but as well with each side needing to gather 7 champions to fight for them that whole process and who either side gets to fight for them would in itself be really interesting.