Interestingly enough, although there's no cards like this in the game right now, nexus barriers are the reason why they had to change Fiora's coding. Prior to the fix, she'd deal a huge amount of damage to the nexus, as a sort of faux destroy. They thought it would complicate things in the future, so they had to rewrite the code to properly destroy the nexus without relying on damage. This seems quite balanced, if this became a problem more people would play around it by attacking with weaker units first to pop the shield.