The main point of DHT implementation is to let run client with full chain even on cheap computers.
As long as you put major load on single node, the hardware requirements for that node grow along with chain. This may bring a situation when only jet set can run full chain. All others will have to blindly beleive to their chain.
This is centralization IMO.
that's inevitable. The block chain is currently > 8 GB. I think things are going to move to an architecture where there a limited set of nodes in the network manage the currency, and most account owners are light clients of some kind. It's simply not practical to have everyone have a block chain. These distributed currencies are just getting started and Bitcoin is already unmanageable.
My vision is 1) no more proof of work 2) distributed rather than decentralized currencies. This offers a lot of advantages.