The idea of your character and skills changing that we always liked, as your character gets stronger and levels up in Tera. We have not played an MMO, where the players start out as a young man or women, maybe 12 or 13 years old. As they level and obtain more skills, the character grows and ages as they progress in the world.
Every ten levels or so, the person could customize their appearance, tattoos, hair style, and facial features. We know this is not a huge one on the game's basic features, but it would add a level of development of your character(tera gold), and we think people would enjoy watching their character grow, as they play.
Certain weapons could be too heavy or big for a young man to use, and until he reaches a high enough level, he can't use certain weapons. Same thing goes for spells, your spells would change in appearance and damage as you level, and the game would constantly be changing as you advance in levels. Something fun to think about, but an idea no developers have done yet.