...OR was he planning on just framing Ethan for being Lark after the meet and just stealing the plutonium again afterwards? Also, how did Walker ensure that Sloane would assign him to Ethan’s IMF group?
shareHe's Sloane's top assassin, presumably a role he's purposely set up for himself so he'd already look like the logical choice as an IMF watchdog.
And while it's not expressly stated, I don't think he ever intended to give back the plutonium. He was a true believer; those bombs were his mission.
Also, I got the impression that his own deal was Lane's freedom in exchange for the plutonium. That's why he lost his sh!t and dropped the franchise's first F-bomb when "Lane [actually Benji]" started waffling.