I'm sure FFG's RPG wing would rather complete all the source and career books for the Edge of the Empire and Age of Rebellion AND Force & Destiny lines before they go full speed ahead into other timeframes and alt campaigns.
There's something to be said about finishing the candy bar you're eating before you start unwrapping another one.
I agree with this at least regarding the career books. New eras would be sourcebooks IMO though maybe a little longer not full rule books. The rules, careers, and such would be the same all the book would need is an explanation of current events and factions, short descs of planets and regions and their alignments, and era appropriate hardware