What i loved so much about DAO was the origin stories (human noble, castless dwarf etc). and thats a reason i didn't really like DA2. having an origin story is what makes the game so personal. these are a few short ideas at what some could be for DA3:
Male human: the choices for human male should be entertwined somehow. for example: prince or thief. here are some stories for those origins:
Human male prince: You are hunting with your knights when you happen upon a small girl wrapped in a cloak. she is blonde and starving and bearly alive. you take her back to your castle where you lay here on a bed in a guest room. later in the evening a ceremony is going to be held to formaly recognise you as Prince of (ferelden, orlais, or where ever you want out of the major kingdoms) you dress for the ceremony and got to the main dining hall. you are also to marry a princess of the neighbouring countrie, whether or not you want to. after the dinner you kneel and are knighted and a crown is placed on your head. just then you see the little blonde girl sitting on the kings dinner chair. she claps sarcastically as the room goes silent, all stare at her. she rises to her feet and declares "yet another leader has been recognised. but it matters not for what follows will be the destruction of you all!" she grabs a knife and stabs the nearest guard. she is knocked out and taken to the dungeons. later that night you are fast asleep when you have a dream. the little girl speaks to you. she mocks you and urges you to wake, for you shant want to miss whats next. you wake, dress and wonder to the window where you see thousands of darkspawn around the walls. the guard captain and twelve other guards come to get you to safety for someone has opened the draw bridge and the creatures are already inside the castle. you are reluctant but you leave via the dungeons. just before you descend into the berial crypts you see the little girl outside her cell. she smiles and says "yet another kingdom falls to me, flemeth, witch of the wilds" and with that she turns into a dragon and destroys half the castle.
Human male thief or female thief: you are the most famous thief in (ferelden, orlais) and you are approached by a shadowy figure who offers you the chance of a lifetime. steal the jeweled crown of the empress (or queen, depends where you are) you accept and enter the castle at night. you sneak past the guards and into the treasury. you see the crown and take it on the way out you are caught, it seems the guards where tipped off by the very person who hired you. they merely wanted you in jail. you're tortured and left in a cell. the person accross from you is either male or female. if your male she is female, and if your female he is male. you talk to this person and find out that he/she was innocent of the crime. you fall in love him him/her and vow to get them out. nut the castle is taken by darkspawn and everyone except you the other prisoner and maybe a certain prince/princess

. the darkspawn can talk and are horiible to the other prisoner using him/her as a prize. you watch as he is murdered or ash she is violated (i dont waant to actually see this but they could use screaming so you know what is happening) as the darkspawn comes to you trick it and steal its sword and escape. vowing vengeance on all darkspawn.