Right now its all about not being on the bottom of the gym. Fix that and watch gyrados and rhydon double weaks dissapearing would be nice.
There needs to be a nitch for other types to get in also. Electric, bug, etc...
Each gym having different tiers by player level, that can be held by any team would have been nice also. Gym lvl a: 5-14, b: 15-24, c: 25-40. Current system has no room for junior players.