Well, not yet. With the overwelming success of these early sales I wouldn't be surprised if they were putting together another expension commanders pack asap with the fan favorites Tiger/Sturmtiger/Jagdtiger/IS-2/Churchill Funnies.
Tiger is 100000% coming as stretch goal, everyone will want it. I would even go as far as saying I'm pretty sure that Tiger stretch goal was planned since the beginning. Not revealing every stretch goal gives them some room to maneuver and see how much more people they can bring in to pledge.