On topic of the thread: It would be best in my opinion to keep it between Bolt and Sarada. Lee's kid would be an acceptable rival too, but I really do not want it to be some random kid that doesn't relate to any of the old Konoha 11. I am fine when a show changes the main characters, but for me the new mains at least have to relate and not feel out of place. Example: Had Akira Toriyama (of DBZ) actually gone through with the plan to make Goten the main character starting with the Majin Buu saga, that would have been fine with me because he is Goku's son. Even if Trunks was the main character that would have been cool because he is the son of Vegeta (the main rival). However, I could not get into it if they picked some totally random new person that doesn't relate at all to the previous cast like Tien's 2nd cousin's uncle's neighbor.
That reason is actually why I couldn't get into The Legend of Korra (that and the guys in the new team avatar all looked the same to me. I couldn't tell them apart)
For these reasons, I think the rival should stick to being Sarada or Lee's kid (as homage to the Lee vs. Neji rivalry), and not some random hyuuga or some other random fodder. Also, to the people saying Chocho or Shikadai, Shikadai seems to lazy to be competitive (like his father) and Chocho seems to care more about food than training or competing (like her father). Neither of them are the rival type. Neither is Inojin, who seems more reserved like Sai.
Bolt/Sarada or Bolt/Lee's kid are the best bets in my opinion.