Raki's purpose you say? It's like Menchi's purpose in exel saga, remember? Emergency food supply (delicasy to boot) for Claire when she will finaly awaken.
Jokes aside i believe it will be the same as most of them said - anchor of Claire's morality and humanity when she is slipping away (and that happens fairly often) and a reminder to her of the Teresa and venegace. Perhaps there will be the choise in the future - save Rakki ot take Priscilla's head just to remind of the Teresa's incident. I would really hate the idea of him becomming the male claymore - there is no way Priscilla would create a threat for her and Easley is too smart for that too. Besides biotechnology is needed to create claymores not just to shove a chunk of yoma's flesh into the body and spill couple of pints of Yoma's blood on top. I doubt any claymore has any knowledge of their creation - there would be the very large probability stray claymores would create others to battle their own creators and awaikened beeings would be able to create armies of underlings as well (as all awakened beeings were claymores at some point and they havent lost a bit of their inteligence upon awakening). At best they would create aready awakened Rakki and that would be pretty awfull setting imo... Well i'd hope the creator wont come up with such perverse idea .