That's actually a really good idea about how to handle curse, I'd much rather it be like that than what it currently is. I love the Ring of Favour and Protection, my first priority when starting a new character is to make a beeline to Lautrec and kill him and equip that ring for the rest of the game. I think Demon's Souls had way more useful rings overall though.
I know this will never happen but I would like to see them get rid of invading or at least make it optional when playing as a human. I'd prefer not having to play offline just to not have some random person invade me. I can count on one hand the number of times I've been invaded and invaded myself in both Souls games, actually I don't think I've ever experienced either in Dark Souls since I'm almost never human and when I am I either play offline or kill myself directly after.
EDIT: I'd also like to see them get rid of weapons with unique powers, they cost far too much durability to be useful. If they didn't replace an attack I'd be fine with them but I don't like giving up the strong attack for some useless special effect.