So I think according to Gary Kurtz one of the original concepts for Episode I was to largely sort of focus on the roots of the Star Wars galaxy/Jedi/Sith/Republic and that the Anakin/Obi-Wan story wouldn't happen until Episode II and wrap up in Episode III. This was back before Kurtz was fired for ESB's budget issues, there was kind of a basic outline for a 9-part saga etc.
Seems like we kind of got this a bit with the finished Episode I, especially in the first half. Obi-Wan is largely a supporting character for most of the film, and Anakin isn't introduced until more than a half hour in (Then again even Luke didn't appear right away in the first movie, although Lucas did intend to introduce him earlier with the deleted Anchorhead/Biggs scenes). So in many ways their story doesn't really start until II anyway. Even Lucas has admitted that most of the story he wanted to tell is in the last two films I think and Episode I had a lot of 'filler'.
Seems that original idea might be what James Mangold is going for (and was also the idea behind the "Dawn of the Jedi" comics and novels).