Well, I wouldn't say 'solved' because the greater scalability issue isn't the resident size of the blockchain, but the real time latency and bandwidth requirements of the network.  I don't even know if there is really much that can be done with 'solving' scalability within the main network itself.  I tend to think that external solutions, such as overlay networks (such as Stratum) taking over a majority of small transactions.  There are a number of ways this can be done, all of which are a balance between the trustless security model of the main bitcoin network against speed and cost, that I think will end up competing in any future that Bitcoin assumes more transaction volume than Visa can deal with.