We discussed this at length in the Suggestions topic, but we moved on from it and I think it's about time to start discussing so we can get them chosen and move on with all the other things we have to do in creating new gym leaders. Here's what was talked about and essentially decided on:

-There will be 12 gyms: 6 in Caldera and 6 in Kirant.
-Hanzo and Mandy were scrapped because their concepts were cliché among some other reasons
-Therefore 6 gyms in Caldera, so that much is done (click the spolier to view them):

-Cetacea and Icthyes are off limits for gyms because of their part in the storyline
-Tristan will be a gym leader, then advance to the E4, so he will fill one of the spots
-It has also been suggested that Layla be removed from the E4 and placed as a gym leader
-It would be nice to re-use Hanzo's sprite, since it's kickass.
-The most recent suggestion (with some edits based on comments afterwards) is as follows:
Kalypso City - Fighting
Portwind City - Light (Tristan)
Sedcini City - Dragon
Laysan Town - Poison
Enechestra City - Rock
Aquapolis City - Dark (Layla)

And the E4 types will be:
Steel
Water
Light
something else

Some possible alterations I can think of would be to ditch Laysan altogether and have a water gym in Gallea, but I can't remember there ever being a poison gym before, so that might be unique. As for Hanzo's sprite, it would be easy to recolour and use as the 'wise old dragon master.'