Given that there are rumors about a possible Obi-Wan movie trilogy, here I will make my pitch in support of such:
1. Ewan McGregor was fantastic as Obi-Wan in the prequels. My judgement may be clouded by my man-crush on him, but so be it.
2. Because the Episode 7-9 characters may have a connection to him. (Ewan had a line of dialogue as Obi-Wan in Ep VII…)
3. Protecting Luke would probably require him to act abroad in the galaxy (especially since the kid’s last name is Skywalker).
4. Great dramatic tension in his conflict between watching over Luke and answering calls for help. The comics have touched on this already some.
5. Bail Organa knows where he is. Episode IV may not be the first time Bail reached out to Obi-Wan for help.
6. Tie the movies to Star Wars Rebels, which covers the birth of the Rebellion.
7. How does he live as a former Jedi who doesn’t use the Force, with Hutts and Sandpeople and no job?
8. Does he still talk to Qui-Gonn? Mace? How does he know that Yoda lives on Dagobah? What if Kenobi visited Yoda? What if Jinn visited both of them?
9. What does he do when he learns that Darth Vader is alive and a scary cyborg? Does he try to stop him? Maybe through a third party, like Black Sun?
10. At some point, the Empire could discover him (probably not on Tatooine) and then pursue him. By sending Vader. How does he escape and protect Luke then?