Re: Pokemon X and Y: Gyms Speculation
The possibilities are Normal, Fire, Water, Grass, Electric, Ice, Rock, Steel, Fighting, Flying, Psychic, Ghost, Dark, Poison, Dragon, Bug and Ground.
Gen V covered Fire, Water (twice), Grass, Normal, Bug, Electric, Ground, Flying, Ice, Poison and Dragon
It is possible that Gamefreak may follow the Johto route and use they types that weren't covered for the next set of gyms.
Thus that leaves possibilities for:
and possibly a Grass and Fire gym as Water was covered twice in Gen V.