Setting: "Lock Difficulty"
When you start a new game, it would be awesome to be able to "commit" to the difficulty setting you've selected and not be able to change it.
I understand all modern RPGs try to secure market share by allowing total n00b players to switch their difficulty any time, so they don't put the game away when they can't beat a part of it. The side effect is that it poses a psychological problem for actual gamers; the problem is that I cannot justify ripping my hair out and grinding to upgrade my character (which are both great reasons to love the game) when I "know" that switching the difficulty option is there and takes 2 seconds.
Peripheral Feature: Provide substantially more content for higher "locked" difficulties
I know witcher 2 provides some really minor (and commonly unknown) "content" additions for higher difficulty levels (i.e. the cursed armor), but I think there should be more incentive to beat the game at higher "locked" difficulty level -- such as more areas, quests, etc., and just general longer gameplay at higher (locked) difficulties.