Update: Could there be more than one Obi-Wan standalone film in the works? a trio of standalone films?
That's what
Cinelinx's source says, with ideas ranging from stories based around Tatooine and/or the Clone Wars, and the return of Qui-Gon Jinn. This could be the basis for a trilogy of unconnected films, or just brainstorming for ideas, it's too early to know for sure.
9/14/14:
Ewan McGregor has made no secret of his interest in reprising the role of pre-Original Trilogy Obi-Wan Kenobi, and now, he may get his chance, as a source with MakingStarWars.com says an Obi-Wan film is in the works. While they were originally planning to avoid any Jedi or Sith characters for the stand-alone films, the character's recent upswing in popularity has led to an art team and a writer working on concepts for an Obi-Wan movie.
(Source:
MakingStarwars.com)