I think the most important thing any game developer can do in this regard is to just add new core elements to the game - I.e. new dimensions of gameplay, as opposed to taking an already existing dimension to new heights.
Yes! That's exactly the side of the problem that I'm attacking. One dimension is the quest oriented gameplay, but now I'm designing a new journey for the character, with a foundation that starts with the player's ambition to enhance his character. I think of it as a strategy game, in which you conquer territory (RPG: level) and then build cities/buildings (RPG: skill hierarchies/perks). The player can "improve" as much as he wants, but if he does it carelessly things can get out of control and enemies will take advantage. If you are a good strategist you don't aim to have the biggest, but to make the most of less. A player might believe that having the strongest warrior he will defeat any super-monster, but the new journey won't have monsters, instead it will have antagonists. My game will confront the player with characters that he just can't defeat with brute and direct force, no matter how high his level is, and the only way around is to be a strategist of skills.