What I mainly want to see are things that haven't been done before. Not just a Dark gym, but an Ice gym that isn't 7th or 8th, a Steel gym than isn't 6th, a Rock gym that isn't 1st, a new female Water specialist, a new male Ghost specialist, an Electric specialist who isn't light-haired, stuff like that.
As for the Elite Four, please let them use types besides the overdone Ice/Fighting/Ghost/Dragon/Psychic/Dark. Just because the Indigo League used those types doesn't mean that every single other E4 needs to have those types, too. I'll still never forgive Hoenn and Unova for so blatantly regurgitating the Indigo E4 types when they could've easily done something else, something that Sinnoh (Bug/Ground/Fire/Psychic) and even Kalos (Fire/Steel/Water/Dragon) deserve kudos for.
And, speaking of the E4, can GF start treating their characters with respect? They're supposed to be the region's strongest trainers, yet are usually more cardboard and less developed than even the most boring Gym Leaders. They were the only important trainers excluded from the PWT, and they're rarely, if ever, seen on the anime.