Saw a video of this rifle on a local forum. Looks like a pretty neat idea. Buy one gun, then you can buy everything needed to change to a different cartridge. The kit they showed had a 223 barrel, bolt, magazine insert and magazine.
The barrel is held in with a nut and there are a couple tools needed to make the changeover. One of them is a preset torque wrench.
Can't imagine it will be inexpensive though. I couldn't tell but I would think the bolt would have to lock into the barrel to be able to change them in this manner.
Also the scope is on a canteliver mount with one end on the barrel, then it swings over to the receiver and one screw from the side secures it there, so each barrel has its own scope.