Hey!
Today I added some more options to the config. You can now separately set how long FFA and Teams games will run (default to 300 seconds). You can also change which type of block will behave as a jump pad(default is slime block), and you can set the strength of the jump pad.

Also, the plugin will save the contents of your inventory as your are joining a game and will return the items to you when the game ends.

Looking toward the future, I've got a few possible improvements in mind. Sorted by how soon I expect to add them.
1. More than 2 teams in Teams mode
2. Custom team names and colors
3. Spectator mode
4. Rather than selecting all players in the world, only players who opt in will be placed in the game (maybe with a join command)
5. Multiple arenas (maybe a voting system to select a map)
6. Multiple games running at one time.