Chord-over-Chord Overlay for Peer-to-Peer networks

In structured Peer-to-Peer(P2P) systems such as Chord or Pastry, each node plays an equal role and has the same responsibility. The most important advantage of such approach is scalability: since there are no centralized resources in the system, the system can easily scale to millions of nodes. However, we need to pay a high price for such scalability, as the maintenance cost of such protocols is very high, especially in a highly dynamic environment where nodes join and leave frequently. On the other hand, Napster-like P2P systems use some centralized index servers for information location and routing services. While such a solution does not scale as well as structured P2P systems, in reality they work very well, since the maintenance overhead is minimal, and the number of nodes handled by each index server in a real system is limited anyway. Can you design a solution that combines DHT and Napster-like architectures so the system is scalable and low-cost at the same time? It is OK to study previous solutions(if available) and make improvements on them. However if you choose to do so, you need to clearly point out this, and discuss the differences between your schemes and the previous ones.