I guess, the only real advantage I see is being able to put a larger variety of barrel lengths on the same receivers. Of course to go < 11" you'd still have to change out the gas system compenents as well.
I don't see that it could be saving much weight from the shortened receiver since it's aluminum.
I might do that if I were just buying one XCR and I wanted to get a PDW, but still be able to use longer barrels.