I read this great quote today, "In their introductory white paper, Danezis and Meiklejohn argue that the bitcoin network suffers from a scalability problem tied to its computationally intensive mining process, by which energy is expended to secure a reliable ledger of transactions."
Do these academics have any idea what it costs to keep the lights on for our current central bank authorities from their briefcases, to their choreographed press releases to their board room meetings and meet-ups, to the banks that administer their bidding and to all of the millions of personnel around the World. I would just wildly estimate it to be about $500M - $1B per day verses Bitcoins $16M per day.
So technically being 2% or less the size of the current framework - " is not scalable" evidently.
I think you're right, there could be unforeseen scalability issues with any new technology - in the same way that nobody thought all the IPv4 addresses would ever be needed. You hear more and more about academic business research on how the blockchain can work. To showcase it's effectiveness as a currency it will also have to be stable and resilient to threats over time.