Also I thnk that Nasuada will become the next rider. Paolini said that the next rider will be a bit of a surprise and Nasuada is possibly Eragon and Mutagh's sister. Also, I believe that the person standing on the beach(Eragon:Deathwatch)is Eragon whilst Roran and Arya walk hand in hand. This thereby(assuming Roran becomes King and Arya becomes Queen of their respective races)would unite the races of Alagaesia. Meanwhile neither is a Rider and Nasuada's dragon is female thereby making Thorne Saphira's mate and turning Murtagh good(he'll either turn good after Galbatorix is dead or during the "final battle"... please gimme some feedback on this extra bit. 
 WRITTEN BY: A HUGE INHERITANCE TRILOGY FAN.