Before revision:  However, a major challenge is to reduce the complexity of layered GCNs and make them parallelizable and scalable on very large graphs --- state-of the art techniques are unable to achieve scalability without losing accuracy and efficiency.
After revision:  However, a major challenge is to reduce the complexity of layered GCNs and make them parallelizable and scalable on very large graphs -- state-of the art techniques are unable to achieve scalability without losing accuracy and efficiency.