OK, wow. Hasbro's aesthetic design team really knocked this one out of the park. This is far more than you'd expect for what's functionally a pretty simple springer.
Good catch. That's good news if true, not becasue Rival barrels would be useful (IMO they wouldn't for most people), but because it means that Hasbro has plans to keep the Rival line around. Hasbro has cycled out ammo formats before, and people would miss Rival.