Yes there would have to be master servers to close this hole, but I can't imagine how it can be done without everybody upgrading to the new client, so we can assume that every Skype user's ip is known or will soon be known. The current state will last for a while.
You don't have to be even logged in for this to work(!) according to some already published research.
You don't have to be even logged in for this to work(!) according to some already published research.