Gameplay elements:
Add a way to upgrade and improve cards in your combat deck. I'd probably just do this through crafting and just leave gear purchasable through money so you have 2 different tracks. Money = gear and crafting = cards. Then you can either sell dropped items for gold or use them in crafting.
Story elements:
Aside from just more places, people, and progression I think I'd just want things to be a bit less linear. For the most part you have to complete nearly all of 1 arc before you can start another. The new elf arc works for this though so I think as more content gets added you might be tweaking things so that multiple things can be occurring at once which I prefer since it makes the world seem more full and alive.