Saga Does Everyone Become A Force Ghost?

To be fair....any apprentice taking out the master is the Sith way....and Vader ended up doing it anyways (though not in the manner he originally intended.)

 

According to the book the legends of Luke Skywalker he can now manifest himself into the good old blue force ghost.

 

You still have to be trained even as the Chosen One. Obi-wan and Yoda taught Anakin how to do it. Lucas confirmed that on the DVD commentary.

He exists where time does not, but that doesn't mean that he can see the correct path that Luke will take. Even Qui-gon couldn't see what path Anakin would take. He even told Yoda that, "There can be many outcomes, but your path is clear." I suspect that certain paths that people can take will be very clear to someone like Qui-gon and Obi-wan, but where there is a clouded path like with the Skywalker men, then that path becomes difficult to see clearly. Obi-wan sees a grim situation because Leia is a captive of Vader and Luke may wind up joining his father. Yet, Yoda still has hope. Possibly that he can sense something that gives him that hope.