I'm stoked for Rambo. He's like the exact character you never knew you wanted but now can't imagine not being a MK guest. His dialogue is going to be epic. His brutalities will be spectacular. He'll be zany and fun and automatically have an edge because he'll trigger all the MK fanboys who hate guests. What's not to love?
As for his move set, there's no reason to expect him to be stiff and clunky like Robocop and Terminator (that wouldn't make any sense), and I honestly don't expect him to be a hardcore zoner either. In terms of MK11 similarities, my guess is that we'll see a blend of Nightwolf, Kano, Sonya, and Erron Black.
Good walking speed and decent dashes. His buttons will feel like a brawler: Quick, forceful hits with an unrefined style, looking to disable his opponent, heavily featuring his knife. Probably no long-range single buttons, but good advancing strings. I don't think he'll be a grappler per se, but I expect at least one true throw string (like NW's s22,1+3) and a command grab that might be a launcher.
He'll have his bow of course. I'd bet on some kind of explosive arrows, probably with slow start-up but fast recovery (think Raiden's lightning bolt), hopefully with the ability to delay or cancel his shot. Won't really zone with it, but will help him with mind games and controlling movement.
He'll have a machine gun too of course, and I'd bet on a MG stance, maybe with a shot count like EB. It'll have a full-auto move, naturally, but I wouldn't be surprised if it arcs up (like Spawn's AA gun) or has a long cooldown/reload, so he can't spam with it. Different ability slots will probably change what his MG stance can do (low shots, faster cancels, etc).
As far as other ability slots, I'd expect see some traps for sure, like EB's beast trap (though hopefully more practical). He might have a mult-hit combo ender special like Sonya's ass whooping. And I wouldn't be surprised to see some version of Sonya's melee parries: fast start-up (to interrupt gaps) but can't be held.
Looking forward to seeing his game play!