Given that the Star Wars RPGs are broken up by thematic campaigns much like the Warhammer 40000 RPG books are, one common type of book that I haven't seen in any line yet has been an Adversaries/Bestiary book.
I would imagine that an Age of Rebellion adversaries book could contain a lot of the elite Stormtrooper units (501st, Nova Troopers, etc), and possibly even include mercenaries and the like that might be locally detrimental to Rebellion forces. There might even be a good argument for putting in local rebel forces that don't answer to Alliance High command.
Just curious to see if anyone else, as potential customers, would similarly be interested in this kind of product.
Finally, I really, really do not want anyone "Plot Critical" to have stats in these books. No Tarkin, no Vader, etc. If the book wants to introduce it's own generals, elite force commanders, and the like, that would be great.