Lot's of ideas.
In my head, I've only concepted the story up to chapter 5. Which, relatively, isn't much. But recently I had a chat with one of my friends who's helping out in the game, and with him I came up with a plot, maybe leading to chapter 10 or 12.
My friend and I also brainstormed some boss ideas and level designs that I plan to incorporate. Some underground stuff, and small on-map minigames in the dungeons.
Lastly, I looked back at old RPGs. If you look at the RPG's nowadays, they're a whole lot easier than they were back then. Reason is, limits, and little guidance. In old games, the game didn't tell you "Go to the castle in the west and bring a fat cow," they made you figure that out, following clues, or just NPCs advice. That's something I'm hoping to use in the game. Another is limits, the majority being Inventory size. What if you were only aloud to have a certain amount of items, depending on the party size? I've been thinking about that too, but I'm not sure if I should use it.
Anyways, that's it for now,