I liked almost all the previous settings that were published under Spycraft Classic or 2.0. If there could be an equivalent to the Adventure Companion with quick setting conversions for ShadowForce Archer, World on Fire, and Dark Inheritance, that would be awesome. But I know that looking backward is not often a good thing. So I would be also thrilled to see an entirely new espionage setting, with adventures and an evolving campaign arc.
And yes, the Agency and Mastermind books, if not de facto
contained in the core rulebook, would be really helpful.
I'm expecting these kind of supplements far more than additional base/expert classes or piles of gear, honestly. I've never been a fan of the Bag Full of Guns series.