I always wanted to play with the character customisation feature. Adding more options for a more varied look.
For example, different coloured skin, hair/styles, wardrobe etc..
I liked that old feature where you could choose which player role you could go with. Adventurer, wizard, warrior and height options for characters.
New NPC's is something that could capture peoples attention. I don't mean just changing the sprites, I'm talking adding a completely new NPC. Maybe a Serpant or gargoyle or something ridiculously cool. That's the thing I like about RSC, your imagination can run away with you and it doesn't sound far fetched.