I would create someone with incredible potential. He/She would be the child of Alucard and Yoko Belnades. That's right you heard me. It would be some time after DoS. Alucard will finally settle down and fall in love with Yoko or some how she would trick Alucard into sleeping with her. No matter how it happens, Yoko would get pregnent and have a child. This individual, when he/she grows into adulthood, would have all of Alucard's and Yoko's powers. I would think that such a person alone could affect the balance of power between good and evil.
Then again, to be realistic and considering how Alucard is, I doubt this would ever happen.