It depends on the deifnition of "hardcore", but if we take it to mean something along the lines of MW2 or COD, ehhhhhh, it'd be hard to manage.
I don't know. Personally, I found it was sometimes frustrating to play a "hardcore game" on the Wii (Redisdent Evil: The Umbrella Chronicles and the Darkside Chronicles) mostly due to controls.
Taking those two as examples, here are the limitations I would imagine that would come up in trying to make a hardcore Kinect game:
-How do I chose movement? Would it be a railroad shooter, as opposed to me chosing the movement by random gestures which are somehow different to the shooting gestures? Or the take-cover-gesture? Or the command-troops gesture?
-Or is it an exploration game like Tomb Raider? The same issues apply with movement control vs action controls. Plus with so many options, it had better be able to differentiate between them.
-I had to sit to play the RE games because they take solid hours of play time to get through fully. I wouldn't play a big "hardcore" title if it means I have to make large gestures constantly to play. Or yell at the screen non-stop.
-Will it be easy to navigate through menus, etc? In a multiplayer match (which most "hardcore" games have) you won't be paused. That means the menus better not be "Paused > Inventory > Weapons > Machine Guns > Ak-47 > Upgrade" with a "wave hand here and wait for 5 seconds to confirm" on each option.
In the RE menus they weren't so bad, bt they weren't that deep and the only things that mattered were the 2 or so weapons you could carry and nothing else. No gem hunting or tool using or questing, etc, so there was nothing more complex to do.
Those are the main issues I can think would possibly come up. Feel free to tell me any more