I agree with the people who said Character customization will be a very good improvement to Pokemon Diamond and Pearl.
People of different races and characters play the Games and they need to express that by showing how they look or how they are different to other people. I'm sure that Nintendo will think this through and let people have this option in the next Gen because most fans are looking forward to this and I'm sure it Isn't that hard to program into the games, as I have seen it featured in a couple of games already.
Another idea is that players could use their Poke money to buy more accessories and clothes for them and their Pokemon, or have certain items unlock certain clothes or hats. Also the main character can only change in houses that lets him or her use their wardrobe.