Add a configurable minimum sell price for specific types of Pokemon, eg. Hidden Ability, shiny, legendary, and maybe even starter. This will make the GTS and pokemon trade economy easier to balance.
2. Min & Max increment
Similar to pixelauctions, GTS needs a minimum bid increment configuration and a maximum as well.
3. A way to disable the announcement
Setting them to "" does not work apparently. I love the announcements, but the only reason I wanted to disable them was because there's no cooldown for the commands (next suggestion) and people can keep on taking down their pokemon and putting it back up to spam.
4. Command cooldowns
I wouldn't be using the cooldown feature if suggestion #3 gets implemented, but some players have suggested it before so I might as well bring it up again in case it was forgotten. This is mainly to limit players on how many they can put in the gts per amount of time.