The biggest problem I see is going to be the sight alignment every time you change the barrels. The is something you can not just eyeball. You would be better served to have a second upper also.
Another problem I see would be the zeroing. A 9mm and 7.62 are not going to have the same zero. I noticed he avoided talking about the issues that I have pointed out. The price is 1299.00. You could just buy an AK and AR and have a rifle for yourself and a family member. I would not waste money on this.
Neat concept, but I'll stick to my AK and Keltec sub 2000 .40. If you were traveling around, with packing and unpacking I'd be afraid I'd lose a piece and then make that caliber weapon system dead.