When the next build goes up with the Editor menu, you can make your own:
- Scenes (what most of the game is)
- Party interactions
- Items
- Enemies, allies, companions
- Species
- Shops
- AI scripts for battles
- Skills
- Bestiary entries
- Background images
- Icons
...I think that's the exhaustive list!
I wouldn't recommend getting into it until then since this original demo (the build that's currently available) is vastly different from the current state of things, and your custom works might not port properly between these versions.